SummaryHematologic data from 1,039 persons who participated in the Miyazaki Cohort study on human T-cell lymphotropic virus type-I (HTLV-I) infection were analyzed. Individuals were classified by HTLV-I antibody status and the presence of abnormal lymphocytes (Ably). We identified several differences in selected leukocyte populations: lymphocyte percent was higher among the HTLV-I carriers with Ably (36.5 ± 2.0%, n = 29) compared with the carriers without Ably (33.1 ± 0.6%, n = 299) and the seronegatives (34.6 ± 0.4%, n = 711) (p= 0.04). Conversely, there was a trend of decreasing eosinophil percent among both carrier groups with the lowest percent among carriers with Ably (1.8 ± 0.5%) compared with the seronegatives (2.8 ± 0.1%) (p = 0.05). Mean basophil percent w, decreased among both carriers groups (p = 0.09). Additionally, red cell count was elevated among the carriers with Ably (461 ±7 x 104/mm3) compared with the seronegatives (446 ± 2 x 104/mm3) (p = 0.03). The HTLV-I carriers with Ably had lower serum albumin (4.39 ± 0.05 g%) compared with the seronegatives (4.47 ± 0.01 g%) (p = 0.10). These alterations may be a consequence of HTLV-I infection, with the greatest changes among carriers with Ably, a subset thought to be at risk for developing adult T-cell leukemia.