The effect of the cholinergic agonist carbachol on a putative substrate for memory (long-term potentiation; LTP) was investigated in slices of rat hippocampus (CA1 region). Carbachol (5 microM) increased LTP when the presynaptic depression of the EPSP was controlled. The results indicate that carbachol enhances the effectiveness of the tetanus, probably through postsynaptic mechanisms. This effect may have implications for the role of acetylcholine in memory and the use of cholinergics in memory disorders.