Sleep loss adversely affects certain types of cognitive processing, particularly associative memory. Given that long-term potentiation (LTP) represents a putative cellular basis of learning and memory consolidation, the influence of sleep deprivation on LTP was examined. Rats were REM sleep deprived for 24, 48, or 72 h using the inverted flowerpot method in temperature-regulated chambers. Hippocampal slices taken from sleep-deprived rats were compared with home cage and pedestal control animals at 5, 15 and 60 min post-tetanization. The results indicated that at 5 min post-tetanization there were no differences in field potentials in any of the sleep-deprived or control groups, suggesting comparable levels of induction. However, analysis of latency-to-peak slope indicated that members of the 48 and 72 h sleep-deprived groups required approximately twice as long to achieve maximum slope as the 24 h group, home cage or 24, 48, 72 h pedestal controls (means 8.17, 7.50, 2.67, 4.67 and 3.17 min, respectively). At 15 min post-tetanization there were no group differences, however at 60 min post-tetanization the slopes of the field excitatory postsynaptic potentials were significantly diminished for the 24, 48 and 72 h sleep-deprived groups (means 30.44, -1.89, 1.47, respectively) as compared with home cage and pedestal controls (means 59.54, 58.42, respectively). This delay in maximal induction, and the degradation of the maintenance phase of LTP, may represent sleep deprivation-induced impairment of the underlying neurochemical mechanisms normally responsible for memory acquisition.