We describe a controlled study comparing the effects on primary care prescribing in west Gloucestershire, UK, where antibiotic workshops were offered, with those in east Gloucestershire, where microbiology tutorials were given. The year-on-year changes in quantity and costs of antibiotics dispensed following general practice prescriptions were measured. There was no significant difference in the number of antibiotic items prescribed across the county, but the number of prescriptions for broad-spectrum agents (quinolones, cephalosporins and co-amoxiclav) declined by 15.4% in west Gloucestershire, compared with a 6.5% increase in east Gloucestershire (P: = 0.002). Use of narrow-spectrum antibiotics (penicillin V, trimethoprim and nitrofurantoin), whose use was encouraged, did not change in west Gloucestershire practices, but decreased by 12% in east Gloucestershire practices (P: = 0.003). There was increased use of clarithromycin and azithromycin in both groups of practices. Antibiotic workshops held in the primary care setting can rationalize antibiotic prescribing. This can reduce prescribing costs and selection pressure by broad-spectrum antimicrobial agents and, perhaps, go some way to reducing the development of resistance.