The pattern of changes in the trypsin-inhibition activities (TIA) of blood plasma, cervical mucus and in the morphological structure of cervix was studied in ewes exposed to 60Co radiation for seven and five days, the radiation doses being 6.7 Gy and 4.8 Gy (700 and 500 R). During exposure, the group of ewes irradiated with 4.8 Gy was given the Roboran vitamin premix in addition to standard feed. After termination of irradiation the animals in this trial were given the ampicillin antibiotic (5250 mg). TIA was determined from the retardation of the hydrolysis of the synthetic substrate N-alpha-tosyl-p-nitroanilide (TAPA) by bovine trypsin; the TIA was expressed as the percentage of inhibited trypsin. As found on the day of the termination of irradiation, almost all the studied TIA values of blood plasma and cervical mucus were increased in the irradiated animals, the range being from 103.1 to 155.0% of the levels for non-irradiated ewes. A reduction was recorded only in total TIA of blood plasma in the group irradiated with the dose of 6.7 Gy (83.1% of the values for non-irradiated animals). In the group of animals irradiated with 4.8 Gy and fed no Roboran, the TIA of cervical mucus was observed to decrease to 92.4%. When evaluating the average TIA of different test groups throughout the experiment it was found that all the studied TIA values of the irradiated animals increased within a range from 104.1 to 184.0% of the values for untreated ewes. It was only in the average values of total TIA in blood plasma that, after irradiation with 6.7 Gy, a decrease to 92.7% of the level without irradiation was recorded. It was found during the study of changes in the proportions of glands in the stroma and changes in epithelium thickness in the mucous membrane of cervix uteri that the irradiated ewes had the epithelium thickness reduced to 95.3%-65.5% and that their stromal gland number decreased to 75.4%-79.7% of that recorded in non-irradiated animals. It was only in the group given a Roboran supplement that an increase to 123.7% of the gland number for untreated ewes was recorded on the tenth day after the termination of irradiation.