The application of in-vitro antifungal susceptibility testing to clinical research and to the guidance of antifungal therapy has been limited by a lack of reproducibility and uncertain clinical relevance. As a result of studies of the identified variables impacting on in-vitro susceptibility results, the National Committee for Clinical Laboratory Standards have proposed a standardized antifungal susceptibility test method M27-P. The degree of intra- and inter-laboratory reproducibility which can be achieved with this method have been defined in multi-laboratory collaborative studies. More convenient methods (microdilution broth and stable gradient technology) have been evaluated relative to the proposed standard method and the potential for a similar process with a disc diffusion method is apparent. A modification of this standard method for susceptibility testing of filamentous fungi appears promising. The existence of a standardized method and of alternative methods with a defined relationship to the proposed standard, facilitates meaningful analysis of published studies addressing the issue of clinical relevance of antifungal susceptibility testing. As a result of this process, correlation of MICs determined in vitro with clinical response to therapy is beginning to emerge, most notably in relation to fluconazole therapy for oropharyngeal candidosis associated with infection with the human immunodeficiency virus.