Various compounds were tested for hymenolepicidal activity against Hymenolepis nana occurring in naturally infested rats. A period of seven days afforded the most critical evaluation of the compounds being tested. Atebrin was the most effective compound followed by Chloroquine. These two drugs were effective in single dose treatments. Dichlorophen was only partially effective in single dose treatments. There was a suggestion of synergism between dichlorophen and Atebrin but no advantage obtained in an Atebrin - Chloroquine combination. Dithiazanine, bithionol and diethyl toluamide were of no practical value.