Objective: To present a repeated test of the quality of ampicillin, tetracycline, chloroquine and ASA from private pharmacies in Laos in 1997 and 1999, and to discuss the quality in relation to the National Drug Policy Programme. Method: A total of 115 of 214 licensed private pharmacies were selected in Savannakhet province, a pilot province in the Lao National Drug Policy Programme. The four drugs, if available, were collected at each pharmacy. Thirty tablets of each drug were taken from a selected container. In 1997, 366 samples were analysed and three hundred in 1999. Identity, assay (content of active component) and measurement of weight variation tests were performed. Drug quality was compared mainly according to the standards of the British and United States' pharmacopoeias. Results: The percentage of substandard drugs decreased significantly from 46% to 22% between 1997 and 1999 (P < 0.001). Substandard ampicillin and tetracycline were reduced significantly from 67% to 9% and from 38% to 12%, respectively (P < 0.001). In total, 3% vs 1% contained no active ingredient, 12% vs 4% had too little or too much active ingredient, and 35% vs 14% had weight variation outside pharmacopoeial limits. Conclusion: Drug quality was improved. However, the prevalence of substandard drugs was still unacceptably high, which may result in adverse clinical effect or treatment failure for individual patients.