The concentrations of lead and cadmium determined by electrothermal atomic absorption spectrometry were significantly higher in the liver and kidney, respectively, of pigs than in their intestinal nematode parasites Ascaris suum. There was no clear pattern in the distribution of lead within the ascarids, but cadmium concentrations were highest in the intestine. A parallel investigation of cattle naturally infected with the liver fluke, Fasciola hepatica, revealed interesting differences. Although the cadmium content of F. hepatica was considerably lower than that in the tissues of cattle, the concentration of lead in the digenean was on average 172, 53 and 115 times higher than in the muscle, kidney and liver of the host. Furthermore, there was a significant positive correlation between the weight of individual F. hepatica and their lead burden. The lack of appreciable heavy-metal accumulation in A. suum is consistent with results for the nematode Anguillicola crassus in fish. However, although lead concentrations in the liver fluke F. hepatica were considerably elevated above host tissue levels, the degree of heavy-metal accumulation was relatively low when compared to that of acanthocephalans and cestodes of fish.