Little is known about the epidemiology of Haemophilus influenzae infections in South Africa. This study was designed to determine the prevalence, serotype distribution, antimicrobial susceptibility pattern and effect of age and hospitalisation on the carriage of H. influenzae in 322 Cape Town children. The overall and type b specific carriage rates in normal children (N = 107) were 45.8% and 4.7% respectively. The yield following nasopharyngeal culture was twice that following throat culture (P < 0.001). Children hospitalised with tuberculosis (N = 62) had significantly greater carriage rates, 66.1% and 37.1% respectively (P = 0.02). Institutionalised mentally handicapped children (N = 77) and children with tuberculosis attending an outpatient clinic (N = 76) had lower carriage rates (P < 0.02). Antimicrobial resistance was a major problem only in children hospitalised with tuberculosis (rifampicin 100%, penicillin 43.9%, erythromycin 85.4%, co-trimoxazole 82.9%). This universal resistance to rifampicin has not been reported previously. There was no difference in the mean age of children with positive or negative cultures, with the exception of those hospitalised with tuberculosis. In this group children infected with type b were much younger (mean 19.7 months) than those with other and non-typeable infections (32.1 months) and the non-infected (50.1 months) (P = 0.04). Duration of hospitalisation or outpatient therapy in the patients with tuberculosis did not influence carriage rates.(ABSTRACT TRUNCATED AT 250 WORDS)