Four representative isolates of Exserohilum turcicum from four major maize growing districts in Uganda were assessed with respect to their cultural variability and pathogenicity towards an isogenic maize series containing the Ht genes for resistance. Two other isolates, one from Zimbabwe and a race 2N isolate from Hawaii, USA, were included for comparative purposes. The isogenic line (H4460), without the Ht gene, developed typical necrotic susceptible lesion type following inoculation with all isolates, whilst H4460Ht1, H4460Ht2 and H4460Ht3 exhibited the resistant chlorotic lesion type. These results indicated that the Ugandan isolates comprised race 0. In vitro studies showed that radial growth rates differed significantly among the isolates, the Ugandan isolates tending to have higher temperature optima than the Zimbabwean one.