The effects of 60Co irradiation on Amblyomma hebraeum Koch, 1844 were studied by mating normal females to males irradiated to attain dosages of 0, 2, 4, 6 and 8 kilorad. The males of all 5 groups were observed mating 7 days after being placed on the host. The higher the irradiation dosage received by the males, progressively longer were the feeding periods of the females mated with them and fewer completed their engorgement. Furthermore, the mass of the females when engorged was lower, fewer laid eggs and the number of eggs they laid decreased progressively. None of the egg batches produced by females mated with irradiated males hatched. No chromosomal abnormalities or discrepancies in spermiophore formation were found in the 2 and 4 kilorad group males, while no micro- or macroscopical growth of the 6 and 8 kilorad group male testes took place, although accessory gland development appeared normal. A. hebraeum males have a chromosome complement of 10 bivalents and a univalent sex chromosome.