Clinical and laboratory findings were examined for 111 human T-cell lymphotropic virus type I (HTLV-I)-infected blood donors. HTLV-I provirus loads in subjects with a family history of adult T-cell leukemia (ATL) or HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) tended to be higher than those in subjects without a family history of these conditions. There were 3 asymptomatic patients with ATL, 4 with a history of uveitis, 7 with hyperreflexia in the lower limbs, and 3 with urinary frequency in the night. The mean CD4 cell/CD8 cell ratio +/- SD was significantly lower (p<.0001) in subjects with hyperreflexia in the lower limbs (1.3 +/- 0.2) than in subjects without any clinical abnormalities (1.7 +/- 0.6), suggesting that subjects with hyperreflexia in the lower limbs already have some immunologic abnormalities. The concordance of HTLV-I infection between husband and wife was lower in this study than in a previous study. HTLV-I-related inflammatory symptoms were more frequent (p =.021, Fisher exact test; OR = 9.5; 95% CI, 1.7-53.5) in HTLV-I tax A-infected donors (3 [50%] of 6 donors) than in HTLV-I tax B-infected donors (10 [9.5%] of 105 donors), suggesting different risks of HTLV-I-related symptoms according to the virus genotype.