The human T-lymphotropic virus type 1 (HTLV-1) was the first retrovirus reported in humans, and it is a cellular transforming agent (BJ Poiesz et al. 1980 Proc Natl Acad Sci USA 77: 7415-7419). It has the capacity to produce tumors of T-cells, neurologic diseases and possibly immunosuppression (M Popovic et al. 1984 Science 226: 459-462). The HTLV-1 has been associated with the etiology of several diseases, such as the adult T-cell leukemia/lymphoma (K Takatsuki et al. 1977 Excerpta Medica: 73-77), HTLV-1-associated myelopathy (GC Roman & M Osame 1988 The Lancet I: 651) and tropical spastic paraparesis (A Gessain et al. 1985 The Lancet II: 407-410). Moreover, an interaction has been observed between retroviral infection and clinical expressions of some diseases such as leprosy, infective dermatitis and strongyloidiasis (L Legranade et al. 1990 The Lancet 336: 1345-1347, A Blank & F Rosso 1996 Acta Medica Colombiana 21: 122-126), that occur occasionally as hyperinfection in carriers of HTLV-1, as in the case of strongyloidiasis. Immunosuppression induced by viral infection may contribute to the development of these disease presentations. Among the inhabitants of the Colombian Pacific Coast there is a relatively high seropositivity of 2.8% for HTLV-1 (G Roman 1988 Ann Neurol 23 (Suppl): s113-s120, C Arango et al. 1990, p. 377-383. In William A Blattner, Human Retrovirology: HTLV-1, Raven Press Ltd., New York). Because tegumentary leishmaniasis is frequent in this area, and presents with a broad clinical spectrum, and subclinical infection is more frequent than the disease, we postulated the possible existence of a relationship between chronic/severe clinical expressions of tegumentary leishmaniasis and coinfection with HTLV-1 evidenced by the presence of antibodies in the serum. We analyzed 92 serum samples from individuals residing in Tumaco (Narino); 23 were obtained from patients with chronic disease (duration of disease > 6 months); 23 from patients with acute disease (duration of disease < 3 months), and 46 from individuals with subclinical infection (positive leishmanin test, without evidence of either active lesions or scars compatible with leishmaniasis). Antibodies to HTLV-1 were detected by latex particle agglutination (Serodia HTLV-1 Fujerebio Inc., Tokyo, Japan). Two samples (2.2%) were positive for antibodies to HTLV-1, one having a titer of 1: 64, and the other 1: 32 (Table). These two sera were confirmed using western blot (Problot HTLV-1 Fujerebio Inc., Tokyo, Japan). Sera are considered positive for antibodies to HTLV-1 when they react with the glicoprotein 46 (gp46) a membrane or envelope protein, and two of the following pro-