The transmission of infectious diseases, mainly hepatitis B, non-A non-B and HIV infection, was the major complication of replacement therapy in hemophiliacs before the introduction of virus inactivated concentrates. The clinical relevance of transfusion associated infections in 43 hemophiliacs treated with different coagulation preparations during an observation period from 1978 to 1986, is discussed. Up to 1981, 38 hemophiliacs have shown hepatitis B seroconversion; 20 of them had a permanent increase in ALT levels. Only two among the five seronegative hemophiliacs showed an immune response to vaccination against hepatitis B. During the observation period 13 hemophiliacs contracted clinical non-A non-B hepatitis. Ten hemophiliacs have been HIV infected. Both hepatitis B and HIV infection occurred more frequently in hemophiliacs treated with foreign concentrates. One patient died of liver cirrhosis, another of AIDS. Since 1986. Swiss hemophiliacs have only been treated with virus inactivated concentrates: therefore no further HIV infections or hepatitis have been observed. Different methods of virus inactivation and factor VIIC purification are discussed. Since factor VIII yield is very low in the ultrapure and virusfree concentrates, a worldwide shortage of factor VIII concentrates is going on. It remains to be expected whether the availability of recombinant factor VIIIC will resolve these problems in the near future.