Alcohol and marijuana are frequently used together, yet there has been little study of how the presence of one drug might affect consumption of the other. The present study examined the effects of alcohol pretreatments on marijuana self-administration in a group of 15 males and 5 females who were users of both drugs. During evening sessions in a recreational setting, pairs of subjects consumed drinks containing 0.0, 0.3 or 0.6 g/kg alcohol 30 min before a 60-min period of ad libitum marijuana smoking. Marijuana self-administration was assessed in several ways: by measuring the number of cigarettes smoked, the increase in expired air carbon monoxide resulting from marijuana smoke inhalation, and the increase in heart rate due to THC absorption. None of these variables was significantly affected by the alcohol pretreatments, although substantial individual differences were observed. These results indicate that low to moderate doses of alcohol do not systematically influence marijuana self-administration.