Investigated the construct validity of the Social Interest Index (SII) on a sample (N = 140) of hospitalized male alcoholics. Because of the inferred properties of social interest, it was hypothesized that the SII would relate positively with measures of some social traits, mental health, intelligence, education, and internal locus of control and would relate negatively with measures of other social traits and MMPI "pathology" scales. The hypotheses generally were supported. The significant positive correlation between the SII and social desirability was discussed along with other theoretical/methodological issues raised by the data.