A data form was devised and used to collect information on clinical cases involving a microbiologist. From the results a relational database management system was created. Of a total of 280 interventions, 137 (49%) were proactive, and in 118 (86%) of these cases the advice given was accepted. The majority of the patients in these cases showed subsequent improvement. Of all the interventions, the given advice was acted upon in 235 (84%), in 22 (8%) it was not and for the remainder this information was not available. This study was a simple method of gaining information on the clinical involvement of the microbiology department of a large city hospital. It provides a reference point from which further research and audit can be based.