From 1996 to 1998, a decline in the rates of donations testing positive for the human immunodeficiency virus (HIV), hepatitis C virus (HCV), and hepatitis B surface antigen (HBsAg) was observed among new donors, while these rates remained stable for human T-cell leukemia/lymphoma virus (HTLV). Among known donors, a decrease was also noted for HCV and HBsAg, while rates remained stable for HIV. No HTLV was detected in 1998 among known donors. Approximately half of the known HIV-positive donors were regular donors (less than two years between donations), as were 88% of those infected with HBV. For HCV, 80% of known donors were occasional donors, the majority of whom had never been screened before. Anti-HBc antibodies were found in 20% of HIV-positive donors and in 22% of HCV-positive donors, and were associated with HBsAg in 99% of cases. Alanine aminotransferase (ALT) levels above the donor exclusion threshold were found in 47% of HCV-positive donors and in 10% of donors with HBsAg. The most common modes of transmission are sexual transmission for HIV (with heterosexual transmission accounting for an increasingly significant proportion) and intravenous drug use, as well as nosocomial infections for HCV. Originating from an endemic country was the primary risk factor identified for HBV. The major risk factor for HTLV is a direct or indirect link to the Caribbean. (R.A.)