Due to technical improvements and new developments of immunological assays, the reliability of serological laboratory diagnosis of HIV infection has improved considerably and the residual risk, due to the diagnostic window for transfusion-transmitted HIV, has been reduced significantly. Through the addition of nucleic acid amplification tests (NAT) to blood donor screening, the residual risk can de further decreased by up to 50%, depending on the sensitivity of the NAT protocol and whether individual or pooled blood donations are screened. In-house and commercially available NAT have been implemented in blood banks as HIV only or multiplexed HIV and hepatitis B or C virus assays. As an alternative to separate antigen and antibody screening, combined fourth-generation assays have been developed in 1997, and have achieved a high degree of sensitivity and specificity. Thus, they can replace stand-alone antigen and third-generation antibody assays. While they are used in the routine diagnostics of HIV infection in many countries throughout the world, they probably represent no alternative for NAT in blood-donor screening in industrialized countries. In the next few years, technical improvements will further simplify NAT screening. While there is still some potential to improve the detection threshold of NAT, the sensitivity of the antigen module of fourth-generation assays (a lowest concentration of 3-5 pg of p24 antigen) is probably very close to its technical limit.