Two hundred and fifty-five isolates of Candida albicans were collected from 93 patients infected with HIV during the course of a clinical trial comparing ketoconazole with itraconazole for the treatment of oropharyngeal or oesophageal candidosis. The susceptibility of the isolates to both drugs was determined by incubating 0.5-2.0 x 10(4) CFU/mL yeast in 0.25-16 mg/L drug in RPMI1640 buffered with MOPS for 24 h at 35 degrees C in 5%CO2 in microtitre trays. Each plate was agitated before reading the optical density. The IC90, IC80 and IC50 were defined as the lowest drug concentration to reduce the optical density to > or = 90%, 80% and 50% of the growth control respectively. IC90S > 0.25 mg/L of ketoconazole and/or itraconazole were found for 42 isolates recovered from 21 patients, 12 of whom had responded to treatment. IC80S > 0.25 mg/L were found for only six of these isolates which had been recovered from three patients, two of whom responded well to treatment. These results indicate that neither the IC90 nor the IC80 are useful in predicting clinical resistance. None of the isolates exhibited IC50 > 0.25 mg/L to either drug which is consistent with the low incidence of resistance reported for these antifungal agents.