Human coronaviruses were found by enzyme linked immunosorbent assay in upper respiratory tract secretions taken during 30% of 108 acute respiratory infections experienced by 30 children under age 6 years with recurrent respiratory infections (index group), and during 29% of 51 acute infections experienced by their siblings. Lower respiratory tract infection--predominantly wheezy bronchitis--occurred in 30% of the index children's coronavirus positive infections but in none of their siblings' infections. Reinfections were common. Two peaks of infection were seen each year in the late autumn/early winter and in the early summer.