The run of autogamy in temperature sensitive mutant ts401, carrying also the mutation of trichocysts nd3a, at permissive (26 degrees C) and non-permissive temperature (35 degrees C) was studied and compared with this process in wild d4-2 stock of Paramecium tetraurelia. The effect of heat treatment on programmed nuclear and cortical events was investigated using cytological silver impregnation Fernandez-Galiano method and immunofluorescence technique with the application of two anti-alpha-tubulin antibodies. The appearance of cells with some large macronuclear fragments and an excess number of micronuclei suggests that nuclear differentiation is inhibited at restrictive temperature and that macronuclear regeneration takes place in this thermosensitive mutant. In such cells impaired oral reorganization was observed. After slight refeeding at the late autogamy, cells stopped at first postautogamous division were induced by heat treatment. The most striking feature of these abnormal divisions was the lack of a basal body duplication wave, which suggests that production of gamma-tubulin, structural protein being the essential component of the microtubule organizing centres, is disturbed at high temperature.