A study was performed to analyse antibiotic usage in a surgical department, with the object of providing a basis for improving antibiotic policies. Patients admitted to the Department of Surgery (134 beds) of the Waid Community Hospital in Zürich (400 beds) after 1st Jan. 1979, and who received antibiotics during the period between 22 Jan. and 31 March were included in the study (n = 154). Daily chartreview provided all necessary information on clinical, diagnostic and therapeutic data of the patients included. 154 patients had 178 treatment courses which were reviewed according to guidelines proposed by the "audits of Antimicrobial Usage" (1977) and categorized as follows: I. agree with indication, appropriate choice and use of antibiotics; II. same, inappropriate choice and/or use of antibiotics; III. administration not justified. 83 of 178 treatment courses were prophylactic and 95 therapeutic. 58% of the prophylactic treatment courses were not justified (cat. III), and the remaining 42% were inappropriate in choice and/or use of antibiotics (cat. II). 41% of therapeutic treatment courses were adequate (cat. I), 43% were indicated, but these patients would have benefited from a more appropriate choice and/or use of antibiotics (cat. II), and in 16% the use of an antibiotic was not justified (cat. III). These results are compared with similar studies. On the basis of our findings, appropriate propositions for improvement of antibiotic policies are discussed.