A polymerase chain reaction (PCR) is described for the detection of the porcine reproductive respiratory syndrome virus (PRRSV). Using the PCR we were able to detect about 30 infectious units of PRRSV resolved in tissue culture medium or sperm. For the detection of PRRSV in sperm the PCR is 10-times more sensitive than culturing in alveolar macrophages. For the detection of PRRSV, PCR provides a good alternative to cell culture methods.