BACKGROUND: Herpesviruses are involved in the pathogenesis of many ocular diseases including keratitis, iridocyclitis, and acute retinal necrosis syndrome. The rapid and accurate diagnosis of herpetic infections has become increasingly important with the rising incidence of immunosuppressive diseases. The purpose of this study was to evaluate the use of the polymerase chain reaction (PCR) to detect herpesvirus DNA in uveitis patients. METHODS: Aqueous samples were aspirated from 11 patients with active uveitis of suspected viral origin. Using PCR, masked samples were assayed for herpes simplex virus (HSV), varicella zoster virus (VZV), and cytomegalovirus (CMV) to assist in supporting the clinical diagnosis of viral aetiology. Masked controls included 10 aqueous humour specimens from normal patients undergoing cataract surgery and specimens from seven patients diagnosed with active non-viral uveitis--Behçet's disease, sarcoidosis, Fuchs' heterochromic iridocyclitis, or Harada's disease. RESULTS: Ten of 11 cases clinically diagnosed as being of possible viral aetiology yielded aqueous PCR positive for a herpesvirus. Eight patients were PCR positive for amplified HSV DNA, of whom two had acute retinal necrosis, one had corneal endotheliitis, and five had recurrent iridocyclitis. VZV DNA was detected in one case of iridocyclitis, and CMV DNA in one case of chorioretinitis. Successful therapy was based on the PCR results. Ten normal aqueous specimens and the seven uveitis samples from cases not suspected of a viral aetiology were PCR negative for HSV, VZV, and CMV. CONCLUSION: These results demonstrate that detecting herpesvirus DNA in the aqueous humour is useful to support a clinical diagnosis of viral uveitis.