This study evaluates multi-attribute utility, a modification of subjective expected utility, as a descriptive model of the adolescent's decision to initiate smoking or alcohol use. According to the model, the young decision maker envisions a set of consequences that will follow the two decision options, either to continue as a nonuser or to initiate usage. Each consequence has three components. The components are the worth of the consequence, which may be positive or negative, the judged likelihood that the consequence will happen, and the importance of the consequence. For a given consequence, the values of these subjective components will vary across individuals, especially those for importances. Within an individual, importances will also change with mood or circumstance, which is how the model accounts for impulsive decisions that may occur in social settings. The model calls for summing the products of the three components, so if any component of a consequence is small, that consequence contributes little to the decision. The model will be tested by eliciting components often independent consequences from a large group of students early in the seventh-grade year. Current usage will also be examined; extant data suggest that most students will be non-users at that time. It is known that a fair amount of initiation takes place during the seventh and eighth grade years. The hypothesis is that those non-users whose model scores are high will be more likely to initiate usage than those whose scores are low. The same students will be queried regarding usage eighteen months later to evaluate the hypothesis. It is now well known that differential knowledge regarding the harmful effects of drug use does not distinguish adolescent users from non-users. The model approach quantifies the idea that anticipated positive consequences play a prominent role in the decision of those who choose to initiate. An important implication is that prevention campaigns might profit by addressing positive as well as negative consequences of usage. [unreadable] [unreadable]