The tissue and blood levels of Cefmetazole are compared after preoperative administration of a single dose of 30 mg/K body weight of the antibiotic administered intravenously (15 patients) and peri-incisionally (30 patients) to patients scheduled for emergency appendicectomy. Local and general tolerance to the antibiotic was good by both routes. No local or general complications arose in any of the patients. As expected, the tissue concentrations achieved with peri-incisional infiltration were significantly higher than those obtained by the intravenous route. With the blood levels, exactly the opposite happens at the start of the operation whereas at the end, there were no significant differences between the two routes employed. The prophylactic administration by peri-incisional infiltration is an easy and safe method which provides high tissue concentrations simultaneously with adequate blood levels and should be considered as useful in the preoperative administration of antibiotics for prophylaxis.