The incidence and clinical features of chronic viral hepatitis B associated with the delta infection were studied in 300 children between one and 14 years in age. Anti-delta was found in 42 (14%) of 300 children with chronic viral hepatitis B, predominantly in patients with chronic active hepatitis who had anti-HBe; exacerbations were found in 11 of 12 children with anti-delta, but in only four of 12 children without these antibodies. These findings confirm the assumption that the process of exacerbation in patients with chronic active hepatitis and anti-HBe may be related to super-infection induced by the delta virus.