The research first examined the occurrence of an opportunity to use drugs by grade level. The study then examined male-female differences in drug opportunity patterns. Results revealed that opportunities to use drugs, and actual drug use, was greater at higher grade levels. In addition, a finding consistent with results in the United States was that males in Panama were more likely than females to have an opportunity to use marijuana, crack cocaine, and other forms of cocaine, but they were not more likely than females to make a transition into drug use once an opportunity had occurred to try each drug. Findings suggested that drug prevention efforts should target youth in lower as well as higher grades, and that efforts to address sex differences in drug involvement also need to act early, at the stage of initial drug opportunities. Findings suggested the desirability of similar research in other countries and pointed to the need to examine factors associated with males' greater likelihood than females of an opportunity to try drugs. Tables, figure, and 18 references (Author abstract modified)