Fluconazole, an orally active antifungal agent, has been shown to be clinically beneficial for maintenance therapy of cryptococcal meningitis. A sensitive gas-liquid chromatographic assay with electron capture detection, which required only a single extraction step and precluded any pretreatment of the chromatographic column, was developed for fluconazole. The assay was linear from 0.1 to 20 micrograms/ml, with a correlation coefficient of 0.999. The intraassay and interassay coefficients of variation were less than 9%. The measured values on average were within 8% of the target values. The extraction recoveries ranged from 87 to 106%. Steady-state plasma fluconazole levels (mean +/- standard deviation) in three AIDS patients with cryptococcal meningitis receiving 200 mg of fluconazole per day ranged from 8.95 +/- 1.32 to 11.41 +/- 0.63 micrograms/ml and were within the expected range for this dosing rate, on the basis of previous studies. The ratio of fluconazole concentration in cerebrospinal fluid to fluconazole concentration in plasma in one patient receiving 400 mg/day was 0.73 at steady state and was consistent with published reports.