A broth macrodilution technique, which was performed by following the recommendations provided by the National Committee for Clinical Laboratory Standards (document M27-P), was applied to study the in vitro activity of itraconazole against fluconazole-susceptible and -resistant Candida albicans isolates from the oral cavities of 100 patients infected with human immunodeficiency virus. The in vitro data demonstrated that itraconazole had good activity against the tested isolates; for 90%o of all strains of C. albicans, MICs were 1 ,Lg/ml, and only one isolate was highly resistant to this triazole (MIC, >16 ,ug/ml). However, the itraconazole MICs for the fluconazole-susceptible isolates were significantly lower than those for the fluconazole-resistant isolates; the MICs for 50 and 90%o of the isolates tested were .0.03 and 0.25 ,ug/ml, respectively, for the fluconazole-susceptible isolates and 0.5 and 1 ,ug/ml, respectively, for the fluconazole-resistant isolates (P = 0.00001). Our findings could be of clinical relevance because human immunodeficiency virus-infected patients who fail fluconazole therapy for oral and/or esophageal candidiasis may require itraconazole at doses higher than those used in standard therapy.Oropharyngeal candidiasis caused by Candida albicans is the most commonly diagnosed opportunistic infection in human immunodeficiency virus (HIV)-infected patients (17). Although this infection is not life-threatening, the sustained immunosuppression seen in these patients facilitates recurrences of infection (9). Consequently, several courses of acuteor long-term suppressive therapy are often required and may contribute to the development of resistant strains (3, 4, 21).Fluconazole and itraconazole are both used either in the treatment of acute oropharyngeal candidiasis or in the prophylaxis of oropharyngeal candidiasis in these patients (1). The lack of standardized methods for in vitro antifungal susceptibility testing presents difficulties in recognizing resistant strains. The Subcommittee on Antifungal Susceptibility Testing of the National Committee for Clinical Laboratory Standards (NCCLS) has recently proposed a broth macrodilution reference method for susceptibility testing of yeasts (10). In the study described here, we investigated the in vitro activity of itraconazole against fluconazole-susceptible and -resistant C. albicans isolates from the oral cavities of 100 HIV-infected patients by using the proposed NCCLS method. patients, and each strain represented a unique isolate from a patient. The isolates were chosen from among all C. albicans isolates sent to the laboratory for in vitro susceptibility testing with fluconazole by a previously published broth macrodilution method (15). In order to obtain isolates of C. albicans with different patterns of in vitro susceptibility to fluconazole, we included isolates for which fluconazole MICs ranged from <1.25 to >80 ,ug/ml. All of the isolates were retested for their susceptibilities to fluconazole and tested for their susceptibilities to itra...