The effects of indeloxazine and piracetam, which reportedly prevent experimental impairments of memory and learning, on long-term potentiation (LTP) of the population spike in the mossy fiber-CA3 system were studied in vitro using the guinea pig hippocampal slices. Indeloxazine (10(-6) M) or piracetam (10(-4) M) significantly augmented the LTP and the effect of indeloxazine on the LTP was approximately 100 times as potent as that of piracetam.