Using 1968 data collected from junior and senior high school students in Bayamon, Puerto Rico, substance usage patterns for heroin and alcohol were predicted for 1975-6. A sample of 1,000 of the initial 5,000 students were selected for re-interview; half were selected to be at high risk of substance abuse and half were selected randomly. Some 657 young people were interviewed, and 130 parents were interviewed when the target young person was unavailable. A 17% prediction of the variance in heroin usage and 33% of the variance in alcohol usage were possible. Two quite different predictive patterns appeared. For the later heroin user, academic failure was the major predictor. Later heroin users tended not to be bothered by nervousness, not anxious about tests, to have parents who generally did not know what they were doing, and to be reserved rather than outgoing in their personality. Other variables predicting heroin usage were poverty, early money-earning, possible deafness, and a rural background. The later heavy alcohol user was most likely male, low on social desirability traits, and low on conscientiousness, but tending to be enthusiastic. Parents tended not to know what their child was doing, and academic achievement was lower than average. (Author/CKJ)