We studied unselected, hepatitis B surface antigen (HBsAg)-positive parenteral drug abusers for antibody to hepatitis D virus (anti-HD) and antibody to human immunodeficiency virus (HIV). The prevalences of anti-HD and antibody to HIV were 67% and 58%, respectively, and there was no association between positivity for these two markers. In a logistic regression model, anti-HD was associated with older age (P = .001), longer duration of drug abuse (P = .045), and the presence of liver disease (P = .002). Antibody to HIV was associated with a younger age (P = .003) and increased serum globulin levels (P less than .001). In patients infected with HIV, the severity of hepatic dysfunction remained correlated with anti-HD. In anti-HD-positive patients, most indices of hepatic dysfunction were similar whether or not antibody to HIV was present, but serum aspartate aminotransferase levels were significantly higher in patients with both anti-HD and antibody to HIV. (124 +/- 16 vs. 74 +/- 11, P less than .05).