One hundred ninety two swine were used in a trial to assess the relative bioavailability of phosphorus (RBP) in six phosphate sources. Phosphates were three feed grade phosphates (FP), two made in Brasil, and one USA made, and three rock phosphate samples (RP) originated from two mines sites in Brasil, and one mine site in Israel. Levels of calcium, phosphorus and fluorine in RP were 29, 12 and 1.7% (RP source 1), 33, 14 and 1.4% (RP source 2), and 30, 14 and 3.6% (RP source 3), respectively. Pigs were fed a corn-soybean meal basal diet (18% CP, 0.95% Lys, 0.75% Ca, 0.37% P) or the basal diet with 0.15% P from a standard purified grade calcium phosphate (SP), or with 0.15% P from experimental FP or RP. Each diet was fed to six pen replicates of four pigs per pen for 35 days (14.4 to 39.9 kg). Weight gain (WG), feed/gain (FG), plasma P (PP), bone ash (BA), and breaking strength of metacarpals and metatarsals (BS-MM) and femurs (BS-F) were improved by phosphorus addition. However, performance and bone parameters were depressed by RP, as compared to FP dietary supplementation. WG, BA, BS-MM and BS-F were regressed to P added, and slope-ratios were calculated to assess RBP in the FP and RP sources. The average bioavailability of P in the FP and RP sources, relative to SP, were 89 and 49% (WG), 112 and 49% (BA), 78 and 28% (BS-MM), and 101 and 52% (BS-F), respectively. Low animal performance and bone strength related to toxicity should be expected if rock phosphates are used to feed pigs. © 2009 Sociedade Brasileira de Zootecnia.3819098Ammerman, C.B., Baker, D.H., Lewis, A.J., (1995) Bioavailability of nutrients for animals, p. 441. , San Diego: Academic Press(1973) Official publication, p. 62. , Charleston: Association of American Feed Control Officials - AAFCO(1995) Official methods of analysis, p. 1025. , Association of Official Analytical Chemists - AOAC. 16.ed. ArlingtonBarbosa, H.P., Fialho, E.T., Gomes, P.C., Efeitos de fontes alternativas de fósforo no desempenho e características do osso de suínos em crescimento e terminação (1992) Boletim da Indústria Animal, 49, pp. 63-72Boyd, R.D., Hall, D., Wu, J.F., Plasma alkaline phosphatase as a criterion for determining biological availability of phosphorus for swine (1983) Journal of Animal Science, 57 (2), pp. 396-401Bowers G.N., Jr., McComb, R.B., A continuous spectrophotometric method for measuring the activity of serum alkaline phosphatase (1966) Clinical Chemistry, 12, pp. 70-89Connerty, H.V., Briggs, A.R., Determination of serum calcium by means of orthocresolphtalein comnplexon (1966) American Journal of Clinical Pathology, 45, pp. 290-296Cromwell, G.L., The biological availability of phosphorus in feedstuffs for pigs (1992) Pig News and Information, 13, pp. 75-78Cromwell, G.L., Hays, V.W., Chaney, C.H., Effects of dietary phosphorus and calcium level on performance, bone mineralization and carcass characteristics of swine (1970) Journal of Animal Science, 30 (4), pp. 519-525Cromwell, G.L., Hays, V.W., Scherer, C.W., Effects of dietary calcium and phosphorus on performance carcass, metacarpal and turbinate characteristics of swine (1972) Journal of Animal Science, 34 (5), pp. 743-751Fernandes, J.I.M., Lima, F.R., Mendonça C.X., Jr., Relative bioavailability of phosphorus in feed and agricultural phosphates for poultry (1999) Journal of Poultry Science, 78, pp. 1729-1736Garzillo, J.M.F., Lima, F.R., Dagli, M.L.Z., Tibial histomorphometry data can explain differences in phosphorus availability in high fluorine rock phosphates (1997) International Congress of the World Veterinary Poultry Association, p. 348. , In: 11., 1997, Budapest, Hungary. Proceedings... BudapestGomes, P.C., Lima, G.J.M.M., Barbosa, H.P., Disponibilidade de fósforo nos fosfatos de Tapira e Fosforindus e na farinha de ossos para suínos (1992) Revista da Sociedade Brazileira de Zootecnia, 21 (1), pp. 83-89Gomorry, G., A modification of colorimetric phosphorus determination for use with the photoelectric colorimeter (1942) Journal of Laboratory Clinical Medicine, 27, pp. 955-960Lima, F.R., Fernandes, J.I.M., Oliveira, E., Laboratory evaluations of feed-grade and agricultural-grade phosphates (1999) Journal of Poultry Science, 78, pp. 1717-1728Lima, F.R., Mendonça C.X., Jr., Alvarez, J.C., Chemical and physical evaluations of commercial dicalcium phosphates as sources of biologically available phosphorus for broiler chicks (1995) Journal of Poultry Science, 74, pp. 1659-1670Mahan, D.C., Dietary calcium and phosphorus levels for weanling swine (1982) Journal of Animal Science, 54 (3), pp. 559-564Maxson, P.F., Mahan, D.C., Dietary calcium and phosphorus levels for growing swine from 18 to 57 kilograms body weight (1983) Journal of Animal Science, 56 (5), pp. 1124-1134(1998) Nutrient requirement of swine, p. 189. , National Research Council - NRC. 10.ed. Washington, D.C.: National Academy of Sciences(2005) Mineral tolerance of animals, p. 510. , National Research Council - NRC. 2.ed. Washington, D.C.: National Academy of SciencesPlumlee, M.P., Jordan, C.E., Kennington, M.H., Availability of the phosphorus from various phosphate materials for swine (1958) Journal of Animal Science, 17, pp. 73-88Potter, L.M., Bioavailability of phosphorus from various phosphates based on body weight and toe ash measurements (1988) Journal of Poultry Science, 67, pp. 96-102Raabe, S., Die beteutung routinemasseger phosphatase bestimmungen in klinischen labors (1955) Recueil des Travaux Chimiques des Pays-Bas e de la Belgique, 76, p. 681(1990) SAS/STAT ® user's guide: statistics, , Statistical Analysis System - SAS. Release 6.04 Edition. Cary