The prime objective of this project is to evaluate and enhance the validity of the Addiction Severity Index (ASI), the most used substance abuse instrument in the world. In the first of two proposed substudies (1a), the construct, discriminant, and predictive validity of the two original ASI summary indices, interviewer severity ratings (ISRs) and composite scores (CSs) will be evaluated and compared with that of two new psychometrically sound ASI summary indices, the clinical factors (CFs) and evaluation factors (EFs). Baseline ASI version 5 and six month follow-up ASIs will be administered to 200 opioid dependent, cocaine dependent, and alcohol dependent patients. A battery of concurrent measures of the ASI problem areas also will be administered at each of the two evaluation points. Treatment attendance and urine toxicology/blood alcohol concentration data will also be obtained for all patients and CDT/GGT for alcohol dependent patients. In a second substudy (lb), the equivalence of standard and abbreviated baseline and follow-up ASIs will be determined for 100 opioid dependent, cocaine dependent, and alcohol dependent patients. The abbreviated baseline and follow-up ASIs will be primarily comprised of the items in the original and newly derived summary indices. Construct, discriminant, and predictive validity of the two original ASI summary indices, interviewer severity ratings (ISRs) and composite scores (CSs) will also be determined in this substudy. The product of the research is the determination of the validity of the ISRs and CSs for the baseline and follow-up ASI-5, establishment of two new, potentially superior, summary indices as alternate measures of problem severity and status for the ASI, and the development of more efficient, abbreviated versions of the ASI that may be used instead of the standard versions.