Adenosine deaminase (ADA; adenosine aminohydrolase, E.C. 188.8.131.52), a purine catabolic enzyme, was studied in Candida albicans, an opportunistic yeast that causes diseases ranging from superficial infections to the deep systemic disease, candidiasis, in immunosuppressed humans. The fungus was grown as a yeast form in LEE's synthetic medium, pH 4.5, at room temperature for various growth periods. Adenosine deaminase (ADA) activity was determined from the cell free extract by measuring the change in absorbance 265 nm resulting from the deamination of adenosine. In yeast form, maximum growth and ADA activity were found at 72 and 24 hours, respectively, whereas in the mycelial form both the growth and ADA activity were maximum after 48 hours. Among the three media tested, tryptic soy broth supported maximum growth and enzyme production, compared to LEE synthetic medium or SABOURAUD dextrose broth. The enzyme was active over the pH range 4-8 and the optimum temperature for ADA activity was found to be 37 degrees C.