I n an earlier investigation hospital infections probably caused by Staphylococcus aureus (S. aureus) were registered in 11%of mothers and infants in the maternity wards of Karolinska Hospital [l]. S. aureus were cultured from 82 % of the infants, 64 % of the mothers and 54 '>A of the staff. Phagegroup I11 strains (particularly those of phage type 47) seemed to cause infection more often than other strains (including strains of phage-type 8OjSl).The frequency of probable hospital infections and of carriers was considered relatively high. I n an attempt to lower this, ordinary soap for hand washing for mothers and staff was replaced with pHiseHex (Winthrop), as this has been reported a valuable hand desinfectant [Z, 31. To evaluate the effect of pHiseHex it was introduced only in the delivery rooms and in one ward while ordinary soap for hand-washing was still used in the other wards. The result of a study of rates of infections and carrier states is presented in this paper.Material, methods and definitions pHiseHex instead of ordinary soap for hand-washing for mothers and staff was used in the delivery rooms and in Ward no I for two weeks before and during the investigation, which lasted one month. In the other two wards ordinary soap was used as before. KO other changes in the ward roiltine were made since the earlier investigations.Infections in mothers and children were registered during their stay at hospital. Infected patients were isolated. On discharge the mothers received questionnaires concerning infections in mothers, babies or other members of their fainilies. These .questionnaires should be returned one month after delivery. Missing or incomplete answers were completed by telephone call.As probable hospital infections were registered:in infants: pemphigus neonatorum, conjunctivitis, sties, umbilical infections and mastitis, in mothers and infants: upper respiratory tract infections with onset in hospital or during the first three days after discharge.in mothers: mastitis (fever, swelling and pain in the breast) and in other members of the family: fiirunculosis, skin abscesses and sties.Cases where it could not be decided whether conjiinctivitis and skin rashes were of infectious or toxic-allergic origin were registered as possible hospital infections, as were cases with breast symptoms without fever (pain with or without rhagades).During the first, second and fourth week nose swabs were taken from all members of