The possible participation of the cholinergic synapses of the hippocampus in the regulation of the learning process was investigated by observing the effect of an intrahippocampal injection of the muscarinolytic atropine on acquisition, consolidation, and extinction. Male Wistar rats were trained for a shock motivated brightness discrimination in a semi-automatic Y-maze. The training was non-stop and continued till the subjects reached the training criterion of performing 10 consecutive runs correctly. The pre-training application of atropine impairs the learning ability significantly, but produces a considerable improvement of retention as compared to the controls. The post-training application of the same dose also produces a considerable improvement of retention. However, when atropine is given 1 min before the first extinction test, no significant effect is observed. It is assumed that atropine has two distinct effects: whereas on one hand it impairs acquisition, i.e., has an aversive effect on short-term memory related processes, on the other hand it has a positive effect on consolidation. It is concluded that atropine has different effects on the various phases of learning. This may be due to changes occurring in cholinergic neuronal activity of the hippocampus during training.