Abstract Seven groups each of ten male and ten female rats received for 90 days either a standard diet or diets containing non-irradiated, 150-krad γ-irradiated or 300-krad γ-irradiated shrimps at a level of 2·8 or 28% on a dry weight basis. No effects on growth, food intake, composition of blood, serum glutamic-pyruvic transaminase, organ weights or histopathology were attributable to the irradiation, but administration of a diet containing 28% shrimps, either irradiated or non-irradiated, affected the relative weights of the liver, kidneys and ovaries. In the liver, fatty vacuolation occurred to an extent which increased with the dietary level of shrimps, but again the effect was no more marked with the irradiated than with the non-irradiated diets.