The acute retinal necrosis (ARN) syndrome is an increasingly occurring entity characterized by the triad of acute confluent peripheral retinitis with papillitis and anterior-chamber uveitis. We present case reports on four patients (age, 12-65 years) with an ARN syndrome caused by herpes simplex or varicella zoster virus and discuss diagnostic and therapeutic modalities. Immediate antiviral therapy in three patients exhibiting the typical clinical features reduced the intraocular inflammation. However, due to proliferative vitreoretinopathy with peripheral retinal necrosis, vitrectomy with encircling band and silicone oil instillation was necessary in all patients. The suspected diagnosis of an ARN syndrome induced by herpes simplex virus (HSV) was confirmed in one case during the early stage of the disease by the detection of increased levels of HSV-IgA in the vitreous and in another case by the measurement of increased titers of HSV-IgG in the vitreous. For the first time, we found intraocular HSV DNA sequences using the polymerase chain reaction (PCR) in one of these patients. In a fourth patient intraocular varicella zoster virus (VZV) infection was confirmed by the detection of elevated VZV-IgA levels and by positive PCR in the intraocular fluids. Two patients who were diagnosed and treated early retained a visual acuity of 0.4 and 0.5, respectively, whereas in the other two patients, whose diagnosis and therapy were delayed (> 6 weeks), visual acuity was reduced to light perception. We conclude that use of the PCR in the intraocular fluids together with detection of autochthonous antibodies in the vitreous seem to be the most important diagnostic laboratory tools.(ABSTRACT TRUNCATED AT 250 WORDS)