A retrospective study of the clinical features in 39 children who were investigated for evidence of Coxsackie B virus (CBV) infection is reported. Eighteen children were found to have serological evidence of infection. An extensive range of features was elicited in both seropositive and seronegative patients, most children complaining of abnormalities referable to muscle and, in particular, of weakness and easy fatiguability. Children with evidence of CBV infection were significantly more likely to belong to social classes I and II, to have relatives with serological evidence of CBV infection, and to show certain dysphoric features as well as to complain of sore throats. The relationship between CBV infection and 'myalgic encephalomyelitis' or 'post-viral syndrome' is discussed, and it is suggested that these descriptions are inappropriate given our current knowledge, and inadequately describe the clinical features seen in the children under study. An alternative description, 'fatigue-dysphoria syndrome' is proposed.