The occurrence of Staphylococcus aureus in the hair of the scalp was investigated in three groups: out-patients, in-patients, and staff of a general hospital. Bacteria were grown from the hair of all the subjects tested and Staphylococcus aureus was the commonest pathogen isolated. It was found more frequently in the hair than in the nose but 20% of hair carriers of Staph. aureus were not nasal carriers. In hospital staff and in-patients, the staphylococci were highly resistant to antibiotics, and phage types usually classified as `hospital staphylococci' predominated. There were more staphylococcal post-operative wound infections in hair carriers than in non-carriers, and in three cases the Staph. aureus was of the same phage type as that isolated pre-operatively from the hair.