<h3>To the Editor.</h3> —Recent reports^1,2indicate the presence of positive human T-lymphotropic virus type I (HTLV-I) antibodies in the cerebrospinal fluid of 16 (73% ) of 22 subjects, and in 94% of the serum samples of Colombian patients with tropical spastic paraparesis (TSP). In a previous neuroepidemiologic study,³we have shown clustering of TSP cases in the southern Pacific lowlands in Colombia, mainly around the port town of Tuma co. However, there are no prevalence studies of HTLV-I or adult T-cell leukemia and non-Hodgkin's lymphoma from Colombia. For this reason, we studied serum samples from blood donors at the San Juan de Dios University Hospital in Bogotá. <h3>Materials and Methods.</h3> —Serum samples from 145 adult blood donors were frozen and transported in dry ice to the Immunochemistry and Clinical Investigations Section, Infectious Disease Branch, National Institute of Neurological Communicative Disorders and Stroke, National Institutes of Health, Bethesda, Md. Serum