Alcohol produces stimulant and sedative effects, and both types of effect are thought to influence drinking practices. This article describes the development and preliminary validation of the Biphasic Alcohol Effects Scale (BAES), a self-report, unipolar adjective rating scale designed to measure both stimulant and sedative effects of alcohol. An initial pool of 12 stimulant and 12 sedative items was derived from previous alcohol effect measures, and from descriptors of intoxication generated by subjects during interviews conducted on both the ascending and descending limbs of the blood alcohol curve. This item pool was administered to a sample of sober college students twice, with a 2-week inter-test interval. Items that were difficult to comprehend, or that had high ratings or low test-retest reliability, were eliminated, resulting in a seven-item stimulant subscale and a seven-item sedative subscale. These subscales showed high internal consistency in a sober state, which was not improved by additional item deletion. The data from this study also provided a basis for revising the instructions for the BAES. The new 14-item instrument was then given to 30 male and 12 female nonalcoholics on the ascending and descending limbs of the blood alcohol curve, after the administration of either 0.75 ml/kg alcohol (males) or 0.65 ml/kg alcohol (females). Internal consistency was high for both BAES subscales on both limbs of the blood alcohol curve (Cronbach's alpha = 0.85 to 0.94), and was not improved by additional item deletion. Factor analyses conducted on both limbs of the blood alcohol curve supported the proposed factor structure of the BAES. A predicted interaction of subscale and limb was observed, with stimulant ratings higher than sedative ratings during rising blood alcohol concentrations (BACs), and sedative ratings higher than stimulant ratings during falling BACs. These data provide some initial validation of the BAES as a self-report measure of the stimulant and sedative effects of alcohol.