Eight patients with recurrent staphylococcal infections, necessitating up to 213 hospital admissions in one patient, gave normal results with the usual immunological investigations, including measurement of serum IgG and IgG₂. In the staphylococcal inhibition test all showed persistently subnormal results, corrected by the addition of compatible normal plasma or normal IgG therapy for 6 months to 21 years, and one died from staphylococcal septicaemia 6 months after withdrawal of treatment. The impairment in anti-staphylococcal response, with failure to produce adequate antibodies, was probably acquired in utero in four patients and inherited in two. In these six patients symptoms started soon after 4 months. In the remaining two the syndrome was acquired later in life.