Niclosamide and cupric acetoarsenite were both effective in removing tapeworm (Moniezia expansa) from unweaned lambs. In four trials there was no significant liveweight gain in niclosamide-drenched, compared with undrenched, animals.Post-mortemexamination for tapeworm showed that although one lamb contained 200 ml (bulk volume) of strobila, 50% of 49 infected animals contained 50 ml or less. The greatest number of scoleces in one animal was 41, and 65% of lambs contained four or fewer.M. expansais not indicated as a cause of diarrhoea in lambs.