Within 3 years 2546 nosocomial infections were registered among 18 897 hospitalised patients of a gynaecological-obstetric university hospital, Results were obtained in a prospective study on the use of nurses specially trained in hygiene. The incidence of nosocomial infections was 13.5% including predominantly asymptomatic bacteriurias and 3.9% without bacteriurias. It was higher after major surgical intervention and lowest in pregnant women, postnatal patients, vaginal deliveries and minor operations. Bacteriurias were the most common infection in all patient groups. They made up 71% of the total, followed by postoperative pelvic infections (7.3%), phlebitis at the site of infusion (6.5%) and abdominal wound infection (4.2%). During the control programme, introduction and reinforcement of various hygienic measures and continuous instruction and control of the wards and treatment rooms by the specially trained nurses the incidence of all nosocomial infections decreased by 48.1% and of urinary tract infections by 42.7%.