A 50-year-old male without relevant past history was admitted because of fever lasting for 23 days. Physical examination showed hepatomegaly and splenomegaly without other findings. Laboratory studies only revealed mildly abnormal hepatic enzymes. The remaining investigations (markers, serologies, antinuclear antibodies, blood and urine cultures) were negative. Chest and abdomen X-ray films were normal. In abdominal echogram a homogeneous liver without space occupying lesions was seen, and computed tomography disclosed enlarged liver, spleen and lymph nodes. Needle hepatic biopsy was reported as showing reactive hepatitis. Although clinically meningeal antibody seroconversions were not found, DNA chains of cytomegalovirus, Epstein-Barr virus, hepatitis B virus and herpes virus simplex were investigated with the in situ hybridisation technique. Its result was a strongly positive hybridisation for herpes virus and negative for the other investigated viruses.