The aim of this study was to further investigate the pathogenesis and epidemiology of feline coronavirus (FCoV)-infections and among others to determine the prognostic value of a positive result in the RT-PCR for FCoV in serum samples collected from cats with abdominal signs. Viral RNA was isolated from 100 microl of serum and subsequently amplified by a nested RT-PCR using primers binding to a highly conserved region of the 3'-end of the FCoV-genome. Sixty-three serum samples collected from 62 cats with abdominal signs were examined by RT-PCR and the clinical outcome was followed up. Four of these cats with a positive PCR-result are healthy more than 70 months after the collection of the blood sample. It can be concluded that viremia with FCoV does not necessarily lead to FIP and death. With respect to diagnosing FIP, a positive FCoV-RT-PCR is of low prognostic and diagnostic value. It can not be recommended to use this assay as sole indication to euthanize cats. Further studies will have to be carried out to demonstrate if the prognostic and diagnostic value of this PCR-assay in other samples such as peripheral blood mononuclear cells is more reliable. However, this method was found to be an important tool to further study the pathogenesis and epidemiology of FIP.