Little is known about the mechanisms of action of kava pyrones which are the pharmacological active compounds of the plant Piper methysticum Forst. We investigated the effects of the synthetic kava pyrone (+/-)-kavain on long-term potentiation (LTP) in the CA1-region of guinea pig hippocampal slices. (+/-)-Kavain reduced the amplitudes of extracellular field potential changes evoked by electrical stimulation in a concentration dependent manner. These effects were reversible. In experiments with LTP no changes were found in the presence of (+/-)-kavain. In conclusion, our findings suggest (+/-)-kavain to be an effective drug in modulating excitatory signals in the hippocampus of guinea pigs. Additionally, no alterations on synaptic plasticity in hippocampal neurons for this kava pyrone can be presumed.