Spontaneous motor activity (SMA) was used to investigate conditioned tolerance to the depressant effect of ethanol, and conditioned responses to stimuli predicting ethanol injection. Rats were injected with saline or ethanol at 800 or 1600 mg/kg, on alternate days, in two distinctly different locations, over a period of 20 conditioning days. The two ethanol doses were administered to separate groups of rats, but conditioned effects were determined by within-subject comparisons. Conditioned SMM responses (rearing and ambulatory activity) were measured after injection of saline in the location previously paired with ethanol treatment, and conditioned tolerance was determined by observing ethanol effects in rats tested in the environment previously paired with saline treatment, Ethanol-paired stimuli increased SMA (both activity measures, both dose-groups) during the conditioned response test. Absence of these conditioned stimuli during the tolerance test resulted in greater behavioral depression with the 800 mg/kg ethanol dose for both the rearing and ambulation measures; however, this effect was seen with the 1600 mg/kg dose for the rearing measure only. These results provide further evidence that Pavlovian conditioning is involved in tolerance to the depressant action of ethanol on overt behavior, and demonstrate the presence of such conditioned compensatory responses in the absence of ethanol treatment. (C) 2000 Lippincott Williams & Wilkins.