1. 1. Oxygen uptake during rest was measured in the water snakes Helicops modestus and Liophis miliaris and related to body size and temperatures between 10-35°C at 5°C intervals. 2. 2. The relationships between oxygen uptake and body size at 25°C is expressed by the relation v ̇o2 = 0.411 BW0.560 for H. modestus and V ̇o2 = 0.339 BW0.647 f 3. 3. The significantly higher b value ( v ̇o2 = aBWb) for L. miliaris may be related to the size attained by the fully grown specimens as well as to the larger lung surface area. 4. 4. There was no significant difference between slopes of males and females despite sexual dimorphism in size in both species. 5. 5. When the exponent b was estimated at various temperatures and compared with the value at 25°C the differences were not significant for any of the species. 6. 6. H. modestus and L. miliaris showed a metabolic plateau between 25 and 30°C, and within this temperature range there were significant differences in the b values between species. © 1980.653367370Aleksiuk, Temperature-dependent shifts in the metabolism of a cool temperate reptile, Thamnophis sirtalis parietalis (1971) Comp. Biochem. Physiol., 39 A, pp. 495-503Baldwin, Oxygen consumption at 20°C in certain snakes Pituophis sayi and Lampropeltis getulus holbrooki with some notes on size and seasonal difference (1930) Iowa Acad. Sci., 35, pp. 313-318Benedict, The physiology of large reptiles (1932) Carnegie Inst. Publ., 425, pp. 1-539Bennett, Dawson, Metabolism (1976) Biology of Reptilia, 5. , C Gans, W.R Dawson, Academic Press, New YorkBuikema, Armitage, The effect of temperature on the metabolism of prairie ringneck snake Diadophis punctatus arny Kennicott (1969) Herpetologica, 25, pp. 194-206Clausen, The effect of aggregation on the respiratory metabolism of the brown snake Storeria dekayi (1936) Journal of Cellular and Comparative Physiology, 8, pp. 367-386Cloudsley-Thompson, (1971) The temperature and water relations of reptiles, , Merrow, WatfordDmi'el, Relation of metabolism to body weight in snakes (1972) Copeia, 1972, pp. 179-181Dmi'el, Borut, Thermal behavior, heat exchange, and metabolism in the desert snake Spalerosophis cliffordi (1972) Physiol. Zoöl., 45, pp. 78-94Fitch, Reproductive cycles in lizards and snakes (1970) Univ. Kansas Mus. Nat. Hist. Misc. Publ., 52, pp. 1-247Galvao, Tarasantchi, Guertzbnstein, Heat production of tropical snakes in relation to body weight and body surface (1965) Am J Physiol, 209, pp. 501-506Graham, Gef, Robinson, Hydrostatic and gas exchange functions of the lung of the sea snake Pelamis platurus (1975) Comp. Biochem. Physiol., 50 A, pp. 477-482Jacobson, Whitford, The effect of acclimation on physiological responses to temperature in the snakes (1970) Comp. Biochem. Physiol., 35, pp. 439-449Jacobson, Whitford, Physiological responses to temperature in the patch-nosed snake, Salvadora hexalepis (1971) Herpetologica, 27, pp. 289-295Kleiber, (1961) The fire of life. An introduction to animal energetics, , Wiley, New YorkParker, (1977) Natural history of snakes, , 2nd edn., British Museum (Nat. Hist.), LondonPough, Heart rate breathing and voluntary diving of the elephant trunk snake Acrochordus javanicus (1973) Comparative Biochemistry and Physiology Part A: Physiology, 44 A, pp. 183-189Rabb, Marx, Major ecological and geographic patterns in the evolution of colubrid snakes (1973) Evolution, 27, pp. 69-83Read, Donnelly, Stratification of blood fow in the elongate lung of the carpet python (1972) J. appl. Physiol., 32, pp. 842-846Ultsch, A theoretical and experimental investigation of the relationships between metabolic rate, body size, and oxygen exchange capacity (1973) Resp. Physiol., 18, pp. 143-160Ultsch, Gas exchange and metabolism in the Sirenidae (Amphibia: Caudata)—I. Oxygen consumption of submerged sirenids as a function of body size and respiratory surface area (1974) Comp. Biochem. Physiol., 47 A, pp. 485-498Ultsch, Respiratory surface area as a factor controlling the standard rate of O2 consumption of aquatic salamanders (1976) Resp. Physiol., 26, pp. 357-369Vinegar, Hutchinson, Dowling, Metabolism, energetics and thermoregulation during brooding of snakes of the genus Python (Reptilia. Boidae) (1970) Zoologica, 55 (2), pp. 19-48Whitford, Hutchinson, Body size and metabolic rate in salamander (1967) Physiol. Zoöl., 40, pp. 127-133Zeuthen, Oxygen uptake as related to body size in organisms (1953) Q. Rev. Biol., 28, pp. 1-12