A longitudinal evaluation was carried out of the clinical, infective, and immunological progress of 34 children (who were aged 6 to 68 months--mean 25 months at the time of writing) born to 31 mothers infected with human immunodeficiency virus (HIV), over a mean observation period of 13.4 months. Clinical symptoms, not always clearly related to HIV became apparent in 11 children, and preceding immune abnormalities were documented in two of them. In eight children culture for HIV was positive, and six of these were symptomatic. No cancers were diagnosed and none of the children died. Immune abnormalities including hypergammaglobulinaemia, IgG subclass deficiency, low serum IgA concentration, antibody deficiency, a decrease in the number of CD4+(T helper) cells, and defective cellular responses to antigens, were found in seven of the children in whom culture for HIV was positive; in two of four who had symptoms and in all four who were symptom free and in whom culture was negative for HIV but in whom HIV antibodies persisted and who were older than 15 months; and in three of nine who were symptom free and in whom culture was negative with loss of HIV antibodies. We conclude that serological diagnosis alone may be misleading and that additional immunological assessment may help to identify affected children. Analysis of humoral and cellular responses to antigens used for vaccination such as tetanus toxoid by measurement of specific antibodies and skin testing are simple and helpful in clinical practice.