The role of different behavioral states was tested with respect to induction and duration of long-term potentiation (LTP), using strong or weak tetanic stimuli of the perforant path input to the dentate gyrus of freely moving male Wistar rats. Recording and stimulating electrodes were chronically implanted into the granule cell layer of dentate gyms and the perforant path, respectively. The effect of tetanic stimulation during three different behavioral states was compared: (a) highly motivated drinking (HMD): Animals (water deprived before experiment 23 h per day on four consecutive days) were tetanized during drinking; (b) high motivation (HM): Animals were treated as the HMD group but received water 1 h after tetanization; and (c) nondeprived controls (NDC). A strong tetanization (10 bursts, 200 Hz) produced a ''saturated'' LTP for more than 24 h, which was not affected by the behavioral state. LTP induced by weak tetanization (3 bursts, 200 Hz), which usually declines to baseline after at most 7 h, was clearly prolonged by HMD (persisting for at least 24 h), but facilitated to a lesser extent by HM. We suggest that a psychological component that arises during drinking after water deprivation triggers mechanisms resulting in an overt strengthening of an ''unsaturated'' LTP after weak tetanization, but without having any effect on a ''saturated'' LTP induced by strong tetanization.