Collection strains representing species belonging to the genus Neosartorya and its relatives from section Fumigati of the genus Aspergillus were compared for some of their phenotypic features. The examination of both the carbon source utilization and isoenzyme patterns provided a useful tool for clustering these strains. Many species (e.g. Neosartorya hiratsukae, N. quadricincta, N. spinosa, N. aurata, N. aureola) could readily be distinguished from other species based on their specific isoenzyme and carbon source utilization spectra. Close relationship was observed between the A. fumigatus and N. fischeri strains. Aspergillus strain FRR 1266, which also revealed distinct mitochondrial DNA and nuclear DNA patterns, and amplified DNA profiles, was the closest relative of the recently described N. pseudofischeri species, and could also be distinguished from the A. fumigatus strains by its specific carbon source utilization patterns. High levels of variability were detected among N. glabra and A. viridinutans strains; most of the strains of Australian origin formed distinct clusters.