A study was made of the combined effects of a number of cholinolytic agents, comprising: atropine, amysyl, BETE (chlorhydrate of the tropine ester of benzylic acid), pentaphene, tropacine, and scopolamine. Substances were given in pairs. Nicotine hyperkinesis in mice was used as an experimental model. The action of the substances was evaluated by Loewe''s method (1928). The results showed that atropine and pentaphene give together caused a rise in the effectiveness of the latter in preventing tremor from nicotine (atropine sensitizes to pentaphene). No such effect was observed when pentaphene was given together with such preparations as BETE and amysyl. Atropine potentiated tropacine; conversely tropacine reduced the effect of amysyl (desensitization). Under these conditions, BETE did not significantly influence tropacine action. The results obtained indicate the very diverse actions of these drugs in producing sensitiziation, desensitization, etc. when given together to animals in which nicotine hyperkinesis had been induced.