Two instruments have been developed to measure social interest, the central concept of Adler's mature system. The purpose of the dissertation was to compare the validities of two measures, the Social Interest Index and the Social Interest Scale. The two primary analyses proposed were the multitrait-multimethod procedure and confirmatory factor analyses. It was hypothesized that both social interest instruments would display convergent and discriminant validity, have more of their total variance attributable to trait than method factors, and not correlate significantly with a measure of social desirability;Ninety-seven subjects were recruited from an alcohol inpatient treatment program at a large, midwestern Veterans Administration Medical Center. The subjects were given the two social interest tests, Edwards Social Desirability Scale, and the Myers-Briggs Type Indicator. Staff members were asked to complete rating scales designed to measure social interest, extroversion, and sensation;Insufficient sample size prevented the application of confirmatory factor analyses to the data. The presence of low reliability coefficients for the staff ratings and large standard errors of measurement precluded the unambiguous interpretation of the results. The Social Interest Index uniformly failed to show convergent or discriminant validity, and correlated highly with the social desirability scale. The Social Interest Scale displayed modest convergent and discriminant validity and did not correlate significantly with social desirability;Factor analysis of the obtained results using the iterative principal axis procedure with varimax rotation produced an interesting three factor solution. The first factor was labeled social desirability-extraversion. The Social Interest Index loaded most heavily on Factor I. The second factor consisted primarily of the staff rating method. The third factor was defined by its most prominent loading, the Social Interest Scale;Due to the consistency of the results in favor of the Social Interest Scale, it was concluded that the Social Interest Scale was a better measure of social interest than the Social Interest Index.