The effects of scheduling the availability of ethanol on its voluntary consumption by the selectively bred alcohol-preferring P rats were examined under three conditions: unrestricted 24 hr/day access (Condition A), access limited to a continuous 4 hr/day (Condition B), and access limited to 1 hr every 3 hr, 4 times/day (Condition C). Food and water were always available. Daily alcohol intakes (mean +/- SEM) with Conditions A, B and C were 6.9 +/- 0.2, 2.1 +/- 0.2 and 4.4 +/- 0.2 g/kg, respectively, while the intake per hour of availability increased from 0.3 +/- 0.03 under Condition A to 1.1 +/- 0.4 g/kg under condition C. The amount of ethanol consumed per drinking episode under Conditions A, B and C were 1.1 +/- 0.1, 2.1 +/- 0.2 and 1.1 +/- 0.03 g/kg, respectively. Mean blood alcohol concentrations (BACs), determined periodically during the dark cycle of Condition A and five minutes after drinking episodes under Conditions B and C, were 59 +/- 10, 61 +/- 7 and 62 +/- 7 mg%, respectively. When unlimited access was reinstated after Condition C, daily alcohol consumption returned to a level similar to that under the initial Condition A (7.2 +/- 0.5 g/kg). When the ethanol concentration was increased from 5 to 20% (v/v) under Condition C, the amount of ethanol consumed per episode at 5% was significantly less than at the 10, 15 and 20% concentrations, and the volume consumed was significantly lower at the 20% concentration than at the 5, 10 and 15% concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)