The Bureau of National Health Insurance (BNHI) of Taiwan issued a new reimbursement regulation effective from 1 February 2001 forbidding the use of antimicrobials in ambulatory patients with upper respiratory infections (URI) without evidence of bacterial infection. We evaluated the effect of this regulation by analysing changes in the types of infections diagnosed and the amount of antibiotics prescribed in 1999, 2000 and 2001. Between 1999 and 2001, antimicrobials for respiratory infections decreased from 18.0 to 9.97 DDD/1000 per day or by 44.6% (P = 0.0000(+)). Antimicrobials for URI decreased from 8.32 in 1999 to 3.28 DDD/1000 per day in 2001 or by 60.6% (P = 0.0000+); from 2000 to 2001 the decrease was 55.8%. Reduction of antimicrobials for URI from 1999 to 2001 accounted for 62.8% of the reduction of antimicrobials in respiratory infections or 51.3% of the total reduction of antimicrobials. Reduction in aminopenicillins was responsible for most of the decrease. (C) 2004 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.