Primary varicella-zoster virus (VZV) infections in adults generally follow a more severe course than in children and are more often associated with life-threatening complications. In the years 1992 to 1995 we observed 7 immunocompetent adults with a severe course of primary VZV infection. All 7 patients presented initially with a characteristic rash. In 6 patients the diagnosis of VZV was confirmed by ELISA on material taken from the lesions, and in all of them it was confirmed by serology. The following complications were observed: pneumonia (5x), elevated liver enzymes (4x), myocarditis (1x), encephalitis (1x) and myelitis (1x). Pulmonary lesions were characterized by bilateral interstitial infiltrates on chest-x-ray and required mechanical ventilation in 2 patients. The liver enzymes were only slightly elevated and clinically not significant. Myocarditis in one case was postulated in view of elevated creatine kinase levels, ECG-repolarization changes and AV-block III which required the insertion of a transitory pacemaker. Encephalitis presented as abnormal behaviour at work followed by seizures. Myelitis was suspected due to ascending sensory motor tetraparesis and confirmed by MRI. All patients were treated with high doses of parenteral acyclovir (3 x 10 mg/kg body weight i.v. per day) for 5-12 days. 6 patients recovered completely and only the patient with myelitis has residual neurological deficits 3 months after discharge. Although we cannot exclude the possibility that supportive therapy without acyclovir would have had the same outcome, we recommend high-dose parenteral acyclovir for treatment of visceral and neurological complications in primary VZV infections in adults.