The effect of nutritional factors in a new culture medium (BW3) is described for the cyanobacterium Nostoc sp. The growth of Nostoc sp. was higher in BW3 than in control media currently used for cyanobacteria. With medium BW3 the content of the pigment c-phycocyanin depended on the culture conditions employed, particularly the nature of the nitrogen and carbon sources. Higher amounts of c-phycocyanin amounting to 20.1% on a dry-weight basis were accumulated when both sources were supplied in the gas phase of the culture. The phycobiliproteins of Nostoc sp. were resolved into two components: c-phycocyanin (λmax = 614 nm) and allophycocyanin (λmax = 652 nm). The phycobiliprotein composition was 30% allophycocyanin and 70% c-phycocyanin. The culture of Nostoc sp. in BW3 medium seems promising as a source of biomass for the production of natural dyes.Centro de Investigación y Desarrollo en Fermentaciones Industriales