The tapeworm Moniezia expansa and naturally infected sheep were investigated with respect to their lead accumulation. Lead—Pb(CH3COO)2 was added to the distilled water and administered orally to the sheep every day for a period of 1 week. After the exposure period the sheep were killed. The impact of an infection with the cestode and a simultaneous Pb exposure, on the concentrations of heavy metals in the host kidney, liver, muscle, blood and cestodes was studied. The concentration of lead in the cestodes was on average 458, 5 and 4-fold higher in the cestodes than in the muscle, liver and kidney of the host, resp.. Parasitised sheep accumulated significantly less lead in their tissues than their uninfected conspecifics (P< 0.05). The differences between host´s tissues and tapeworms were found to be significant (P< 0.05). This study reveals that lead accumulation also occurs in cestodes parasitizing mammals.