Two infants with roseola infantum and meningitis caused by human herpesvirus-6 infection are reported from the Department of Pediatrics, College of Medicine, National Taiwan University, Taipei, Taiwan. A 7 month old girl presented with fever, bulging anterior fontanelle and mild hepatomegaly. Lumbar puncture showed 18 mononuclear and 2 polymorphonuclear cells/mm3 and CFS protein of 0.35 g/1 and glucose 3.05 mmol/1. The first serum on the 4th day of the illness was positive for IgM anti-HHV-6 (titre 1:10), and the second serum taken 11 days later was positive for both IgG and IgM anti-HHV-6 (1:160 and 1:80 respectively). A maculopapular rash appeared on the face, scalp and neck on the 4th day of illness. Case 2. A 4 month old boy presented with cough and high fever and 4 episodes of generalized seizures in the next 2 days. CSF examination on the third day revealed 8 polymorphonuclear cells and 1 mononuclear cell/mm3. CSF protein and glucose were normal. A blood smear revealed lymphocytosis. Liver function tests were abnormal. A rash appeared on the 4th day and fever subsided. The first serum was negative for both IgG and IgM anti-HHV-6 and the second serum taken 12 days later was positive for both (1:160 and 1:40 respectively). The boy recovered without sequela. 
COMMENT. The illnesses linked to human herpesvirus-6 infection have included roseola infantum, hepatitis, lymphadenitis and mononucleosis. Roseola infantum is the infectious fever most commonly associated with febrile convulsions. In a review of the literature over 3 decades (1934-64) of 3,168 patients reported in 13 publications, roseola infantum was the cause of febrile convulsions in 4% (range 0.6 - 7.6%). The average incidence of convulsions among 581 patients with roseola infantum reported in 11 publications was 22%. The evidence for an encephalitie process such as CSF pleocytosis was lacking except for a rare case and the height of the body temperature that usually accompanies roseola infantum was considered sufficient to explain the frequent complication of convulsions . The present report of HHV-6 infection associated with roseola infantum supports the theory of an encephalitie illness in the etiology of the seizure. Inclusion of roseola infantum as a cause of simple febrile seizures must be reevaluated in the light of this report.