Morphological anomalies of the spore forming structures in 13 thermotolerant strains of aspergilli were studied on two different media (Sabouraud glucose and Czapek-Dox agar) incubated at 28 degrees C, 38 degrees C and 45 degrees C. A few more casual observations in contaminant non-thermotolerant aspergilli were also analysed. A logical classification of these anomalies was given, depending on what part of spore forming structure was affected. Some of these anomalies have either never been described before or not yet reported, i.e. in five additional Aspergillus spp. The incidence and relationship to the culture medium and incubation temperature of these anomalies, as well as possible significance of our observations, were discussed.