Long-term potentiation (LTP) was examined in streptozotocin (STZ)-induced diabetic rats of 8 (DM8) and 20 (DM20) weeks duration of diabetes mellitus (DM). DM8 animals showed significant LTP induction, although the potentiation of the synapses was significantly lower than in the control animals. No significant potentiation of the synapses could be demonstrated in DM20 animals. The different aspects of LTP induction in the DM8 animals were studied. The threshold of LTP induction was measured by stimulating the slices with 100 Hz frequency trains of stimuli containing different number of impulses. The results showed increased threshold for LTP induction in the DM8 animals compared to the controls. The late LTP (L-LTP) phase induction was studied by applying 3 repeated HFSs to the afferent fibers. Diabetic animals (DM8) slices failed to maintain the synaptic potentiation induced by the high frequency stimulations (HFSs) for more than 1 h.