Ethanol (EtOH) withdrawal is characterized by a hyperexcitable state that includes anxiety, tremor, muscle rigidity and seizures. The present three experiments examined the effects of EtOH dependence and withdrawal on the acoustic startle response, an easily quantifiable measure of behavioral reactivity to exteroceptive stimuli. Two intensities of startle stimuli, 105 and 120 dB pulses, were presented to rats during chronic EtOH exposure and during EtOH withdrawal. Prepulse inhibition, which is a sensitive measure of sensorimotor gating processes associated with filtering sensory stimulation, was also assessed during chronic EtOH exposure and withdrawal. Prepulse inhibition was induced by the presentation of a weak 80 dB acoustic stimulus 100 ms prior to a 120 dB stimulus pulse. After 14 days of EtOH liquid diet administration the magnitude of responses elicited by 105 and 120 dB startle stimuli was less in ethanol-treated subjects during continued EtOH access than in animals fed a control liquid diet. When EtOH liquid diet treatment was continued for an additional 3-day period and animals were tested 8 h after withdrawal from EtOH, withdrawn animals were more reactive to startle stimuli at both intensities than were animals maintained on the EtOH liquid diet. A time-course experiment with repeated startle testing at 4, 8, and 12 h post-EtOH exposure revealed significant increases in responding to the 105 dB startle intensity at 8 h post-EtOH exposure. The ability of animals to respond to a prepulse stimulus was not affected during chronic EtOH treatment, but was reduced during withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)