Okinawa prefecture is one of the endemic areas for adult T-obtained and were tested. The initial sampling was performed cell IeukemiaAymphoma (ATLL) in Japan. In this study, 2,013 when the children were 3 years old, and the final sampling serum specimens drawn serially over a period of I5 years when they were 18. (1968-1983) from 311 motherlchild pairs in Okinawa were tested for antibodies to human T-cell leukemia virus type I Defection of H'IZV-I antibodies (HTLV-I) by enzyme-linked immunosorbent assay and by in-The screening test for HTLV-I antibodies was the enzymedirect immunofluorexence. The prevalence rate of HTLV-I linked immunosorbent assay (Taguchi et al., 1983) using the antibodies was 20.9% (65 cases) in the mothers and 3.2% (10 cases) in the children. Of the 65 seropositive mothers, 10 kit of Eitest ATL (E-0733, Eisai, Tokyo, Japan). Serum spec-(15.40/0) had seropositive children. This study revealed a imens showing a 2.5-fold rise in the absorbance value over the icant difference between the prevalence rates of HTLV-1 an-predetermined negative Control Samples underwent Confirtibodies in mothers and children. In addition, children born to matory testing. The confirmatory testing for HTLV-I antibodseropositive mothers had acquired their HTLV-I antibodies by ies used was the indirect immunofluorescence method (Hinuma the age of 3 years, and were still seropositive at the age of 18 et a/., 1981). MT-1 cells, a T-cell line derived from a patient years. No initially seronegative child was found to have sero-with ATLL (Miyoshi 1980), were used for the indirect converted during the period investigated. (1982).