The mycelial and yeast forms of the fungus Paracoccidioides brasiliensis were cultured in a chemically defined liquid medium with different iron concentrations and the growth measured spectrophotometrically. The iron binding capacity of culture supernatants was measured by a colorimetric assay. Both the mycelial and yeast forms were able to grow in media containing trace amounts of iron (0.02 mgl-1) but when the iron chelant 1.10 phenantroline was added there was a delay in the initiation of growth of the yeast and almost total inhibition of the mycelium. When iron excess was added to media containing phenantroline, this inhibitory effect was reversed, partially for the mycelial, and completely for the yeast form. For both mycelial and yeast forms, the iron binding capacity of the culture supernatants was greater in media with low iron concentrations.