In a pilot project (INTERUNI-II), we collected retrospective data from eight university hospital pharmacies covering the period from 1998 to 2000 to obtain estimates for the antibiotic use densities in the surgical services of teaching hospitals. Antibiotic use data were obtained from hospital pharmacies and expressed as prescribed daily doses per 100 occupied bed days (PDD/100). The definition of prescribed daily doses was according to guidelines for antimicrobial therapy in adults with normal renal and hepatic function used in the participant hospitals. We separately assessed means and ranges of antibiotic use densities for surgical intensive care units (SICU), and other surgical wards (OTHER SURG). Overall antibiotic use densitiy (3-year average) in surgical departments was 38.7 PDD/100, with a slight decrease during the observation period (1998: 37.3; 1999: 39.1; 2000: 39.6 PDD/100), respectively. Values ranged between 26.7 and 45.1 PDD/100 for the individual hospitals. Antibiotic use was higher in SICU areas (3-year average, 99.5; range, 56.1-137 PDD/100) than in OTH SURG (3-year average, 32.4; range, 18-41.9 PDD/100). The proportion of oral antibiotics in OTH SURG ranged between 26.1 and 57.4% (mean, 42.8%). Betalactam antibiotics were the most frequently prescribed drugs. 33% of betalactam PDD belonged to the class of broadspectrum betalactams (range, 21.5-44.8%). Fluoroquinolones were the second most prescribed drug class. They were more frequently used than aminoglykosides. There was considerable variation between participant hospitals in the use of specific drug classes in given patient care areas.