This study assessed the potential pharmacokinetic interaction between rifampicin and ketoconazole, two drugs used to treat the increasingly common combination of Mycobacterium tuberculosis and Candida albicans infection in AIDS patients. The peak plasma rifampicin concentrations in six healthy male subjects were not altered when taken in conjunction with ketoconazole. However, the peak plasma ketoconazole levels were significantly diminished when taken in conjunction with rifampicin, compared to when taken alone (P less than 0.015). The mean area under the curve (AUC) for ketoconazole was significantly diminished when taken with oral or intravenous rifampicin (P less than 0.001).