Subsequent to the National Epidemiologic Surveillance Program developed in 1997 by the National AIDS Program, anti-HTLV-I/II antibodies among blood donors in Santa Fe Province started to be detected. On the basis of this initial finding, it was regarded of interest to evaluate the true HTLV-I/II seroprevalence in this population during a four-year survey. Thus, from 1997 up to 2002, 9425 samples were studied from 17 out of the 19 provincial departments. Out of the total sampling, 38 proved reactive by agglutination techniques, 18 of which were confirmed by western blot (WB). Out of the latter, 10 were HTLV-I/II seropositive with a final prevalence of 0.1% (10/9425), whereas 7 were indeterminate and 1 negative. Among these 10 confirmed sera, 2 (0.02%) were HTLV, 3 (0.03%) HTLV-I and 5 (0.05%) HTLV-II. It should be highlighted that the presence of HTLV-I/II infection in blood donors in Santa Fe Province was demonstrated for the first time, with a prevalence greater than that reported for blood donors in non-endemic Argentine areas. Such findings confirm the need of corresponding systematic screening through regulatory blood bank norms in Santa Fe Province.