1. Injection of oxotremorine in the rat results in tremor and an increase in brain acetylcholine. The effects of atropine and dyflos have been investigated on both these actions.2. Atropine decreased brain acetylcholine concentration and inhibited oxotremorine-tremor. It did this in doses which did not prevent the oxotremorine-induced increase in whole brain acetylcholine.3. Dyflos increased brain acetylcholine concentration, but it was without effect on oxotremorine tremor. Some mutual antagonism was observed between the actions of oxotremorine and dyflos on rat brain acetylcholine concentration.4. These results do not support a causal relationship between the increase in whole brain acetylcholine and the tremor produced by oxotremorine.