Effects of a new thyrotropin-releasing hormone (TRH) analog, N alpha-[[(S)-4-oxo-2-azetidinyl]carbonyl]L-histidyl-L-prolinamide dihydrate (YM-14673), which improves experimentally induced memory dysfunction, on long-term potentiation (LTP) in the mossy fiber-CA3 system, were investigated using guinea pig hippocampal slices. At concentrations of 10(-7) M and 10(-6) M, YM-14673 significantly augmented LTP in a concentration dependent manner. The magnitude of effect of 10(-6) M YM-14673 was similar to that of 10(-6) M TRH. As LTP in the hippocampus is regarded as an elementary process of memory and learning, the augmenting effect of YM-14673 on LTP in the present study may contribute to this drug's ability to remedy memory dysfunction.