The following hypothesis has been tested: sensation seeking, A-state and A-trait, and depressive mood should positively affect adolescent substance use. The personality variables and alcohol and drug use were assessed among 1,900 Israel adolescents, 14 to 19 years old. The major findings were as follows: (a) Sensation seeking and availability significantly affected the "ever" and "current" substance use among adolescents. On the other hand, contrary to our hypothesis, neither A-trait nor depressive mood significantly affected substance use. (b) A-State affected the use of alcoholic beverages and nonprescribed medications. (c) The data emphasized the significant role of availability of drugs in the understanding of adolescent' substance use. The implications of these findings for interventions among adolescents are discussed.