The relationship between acute myeloid leukemia (AML), acute lymphocytic leukemia, chronic myeloid leukemia (CML), and refractory anemia with excess of blasts (RAEB) and antibodies to human T-cell lymphotropic virus types I and II (HTLV-I and HTLV-II), and hepatitis B virus and hepatitis C virus (HCV) was investigated in a multicenter case-control study. There were 431 cases enrolled in the study at the time of diagnosis of hematological malignancies, and 862 controls ages 15 years or older were recruited in three hospitals. Antibodies to HTLV-I and HTLV-II, antibody to HCV, hepatitis B surface antigen, and antibody to hepatitis B core antigen were assayed. All cases and controls were negative for HTLV-1 antibodies; one case (1 of 431; 0.2%), and one control (1 of 862; 0.1%) were found positive for HTLV-II antibodies. A nonsignificant excess of risk for hepatitis B surface antigen was present among RAEB cases (odds ratio, 2.40; 95% confidence interval, 0.46--12) CML, (odds ratio, 2.70; 95% CI, 0.86--8.43), and between antibody of hepatitis B core antigen and AML (odds ratio, 1.40; 95% CI, 0.93-2.10). A weak, nonsignificant association was present between AML, acute lymphocytic leukemia, RAEB, and antibody to HCV. These preliminary results suggest a possible association (elevated odds ratios) between hepatitis B virus, AML, RAEB, and CML. However, because all confidence intervals overlapped the null value, these findings need to be confirmed in larger case-control studies.