Adherence to pharmacologic interventions in clinical trials is an issue of major concern to clinical investigators. This proposed study will examine the effects of two strategies of inducing enhanced adherence to medication in the context of a clinical trial: habit training vs habit training plus problem solving. Based on the behavioral principles of stimulus control and anticipatory problem solving, these adherenceinducing strategies are devised to address common reasons for poor adherence. The clinical trial, which is funded by the NIH, utilizes once daily doses of lovastatin or placebo to reduce cholesterol. We propose to use a randomized, two group design, involving 150 subjects per group. Within each of the groups, half of the subjects will be on lovastatin and half on placebo. The main outcome measure is medication intake monitored daily and unobtrusively with the MEMS electronic monitor. For each subject, event time series of six months duration will be obtained. The effect of these interventions will be determined on (1) average adherence at two and six months; and (2) variability of adherence. In addition, (3) the relative cost effectiveness of each intervention will be examined by a recalculation of sample size needs based upon increased adherence and related cholesterol lowering. Ancillary goals of the study include determining (a) components of variability of medication intake using statistical modeling techniques; and (b) covariates of treatment effects including baseline daily hassles, problem solving skills, and generalized expectancy for success. The interventions, implemented at the outset of pharmacologic intervention within the clinical trial, are timed to yield maximum effectiveness. Such randomized induction studies have not been undertaken. By capitalizing on a new unobtrosive assessment technique that generates the timing of medication intake over prolonged periods, the proposed study will produce a unique set of data suitable for the study of recurring cycles in medication intake patterns.