In a longitudinal study of precursors of drug usage, data collected in 1968 on health variables was related to substance usage patterns obtained in 1975-76. Some 657 young Puerto Ricans were interviewed for this study, drawn from a pool of about 5,000 questionnaired in 1968. The major findings were that the health factors associated with drug involvement were mainly those of habit and fatigability. Other factors which could be used as descriptors of specific substance users included sensory impairment and digestive problems as well as not having psychosomatic or mobility problems. The best predictors were found in the area of: habits, especially sleeping patterns; facial appearance; sense receptors (eyes, ears); mobility and activity restrictions; heart trouble; nervousness; and the taking of prescription medicines or pills. The highest number of associations as well as the best predictive ability was found in the marijuana and alcohol groups. The least amount of significant relations and predictors was found in the realm of heroin use. (Author)