The author describes and evaluates different approaches in laboratory diagnosis of HIV infection and AIDS. Serological detection of anti-HIV antibodies provides despite some limitations very good diagnostic opportunities. ELISA screening tests supplemented by confirming tests, in particular the Western blot, ensure maximum accuracy of the obtained results. Evidence of the viral antigen in serum is used as a diagnostic criterium only in special instances and serves rather for monitoring of the state of HIV infected subjects than screening for new cases of infection. Cultivation of the virus from clinical material is difficult but in some instances, e.g. in neonates and young children it is the only evidence of HIV infection. Recently for diagnostic purposes molecular biological methods are used, in particular amplification of proviral DNA by a polymerase chain reaction. Their application is, however, so far restricted to research departments because they are technically and economically pretentious.