Changes in the length of oestrous cycles, plasma progesterone and oestradiol-17 beta levels were monitored for 6 months in Trypanosoma congolense-infected normocyclic small East African goats obtained from three tsetse-endemic areas and one tsetse-free area of East Africa. Irregular oestrous cycles were observed in all infected goats, before cessation at the second cycle post-infection in the more susceptible and fourth cycle in the more resistant goat groups. A significant decline in the progesterone and oestradiol-17 beta parameters were observed. The decline in hormonal values was, however, less in the more resistant than in the susceptible goat groups at least in the first 2 months post-infection. Resumption of the ovarian cycle were observed in few resistant goats after 5 months of the infection. It is concluded that clinical tolerance is correlated with residual fertility, i.e., the greater the tolerance the higher the retention of fertility.