Since the development of the highly sensitive polymerase chain reaction, PCR has been increasingly used for the diagnosis of viral infections, including the detection of human immunodeficiency virus (HIV), the causative agent of AIDS. In our laboratory a diagnostic PCR is carried out on proviral HIV-1 DNA using a standardised algorithm based on three HIV-1 primer sets. The three primer sets, amplifying a fragment in the LTR-gag gene, in the pol gene and in the env gene, are situated within conserved regions of the HIV-1 genome. These primers allow us to detect not only HIV strains from Belgian patients but also from African patients, who are, for historical reasons, a substantial part of the HIV-positive patients in Belgium. We are able to detect 1-5 copies of proviral HIV-1 DNA with each of the three nested primer sets. A sensitivity and specificity of 92 and 100%, respectively, were achieved when testing 24 Belgian and African HIV-1 seropositive samples. In our lab, the same PCRs are also used for the detection of viral RNA in cases of a doubtful undetectable viral load when using a commercial HIV-1 viral load assay. This is because present-day commercial assays are not entirely reliable with divergent strains. Both our 'in-house' diagnostic DNA and RNA-PCR can also be used semiquantitatively with limiting dilutions.