The mating type distribution among the 28 Histoplasma capsulatum isolates obtained from the histoplasmosis outbreaks which occurred in Indianapolis in 1978-1979 and 1980-1981 was studied. The overall ratio of + and - types was 1:2.5. The isolates from disseminated patients showed a 1(+):1(-) ratio while the isolates from non-disseminated pulmonary cases showed a 1(+):4(-) ratio. The frequency of the + type in these outbreaks was three times higher than that of the previous study. This was due to an unusually high prevalence of the + type among the patients with disseminated histoplasmosis.