Subsamples of drug users and nonusers are also included. Comparisons across the age range studied (10 to 29 years) showed how subjective meanings and the system of mental representation, including those characteristics of drug users and nonusers, evolve as a function of age. Based on the domains studied, the distance measured between user/nonuser groups and between age groups showed systematic and predictable increases that reflect on construct validity. The perceptual and motivational dispositions identified correlated significantly with drug use (behavioral validation). Free associations revealed a close relationship between drug use and such psychological dispositions as dominant perceptions, attitudes, and systems of mental representations. The results provide new insights into the role of such variables as perceived harm and subjective appeal. They suggest the desirability of developing prevention programs designed to change those perceptual and attitudinal dispositions associated with drug abuse. 41 references and 5 figures