The timing of surgical antimicrobial prophylaxis was determined before and after an intervention programme of education of surgeons, anaesthetists and nurses on the subject of antimicrobial drug prophylaxis, and the subsequent implementation of new protocols of single dose prophylaxis administered within one hour before incision. This prospective study was performed in three surgical departments of a university hospital. For comparison, the timing of prophylaxis was also determined in an operating department of a community hospital. The timing improved considerably in the departments of the university hospital where the intervention was carried out: administration of the first dose within one hour before incision increased from 39% to 69% in department A and from 64% to 80% in department B. Before the intervention, seven out of 16 prophylactic doses were given after inflation of the tourniquet. After the intervention all doses of prophylactic antibiotics were administered before inflation of the tourniquet. Initially, the intervals of multidose prophylaxis varied widely. In the second review, single-dose prophylaxis increased from 21% to 78% in department A and from 31% to 85% in department B. We conclude that the intervention succeeded in improving the quality of surgical prophylaxis.