Among 29833 donors evaluated we have found a prevalence of 1.52% for HBsAg and 11% for anti-HBc. The co-positivity anti-HBc/anti-HBs in 2783 donors HBsAg negative/anti-HBc positive was 81.9%. The prevalence for HBsAg is low among Campinas donors, while anti-HBc presents high prevalence when compared to that of other countries. The anti-HCV detection in blood donors of Campinas has shown a positivity of 2.6% which is much higher than that of USA and Europe. About 36% of the anti-HCV positive donors are anti-HBc reagent, leading to the conclusion that these two "viruses" infect simultaneous or sequentially Brazilian blood donors.