SETTING: Quality assurance for the World Health Organization (WHO)/International Union Against Tuberculosis and Lung Disease (The Union) global tuberculosis (TB) drug resistance surveillance programme. OBJECTIVE: To monitor the quality of drug susceptibility testing (DST) in different countries. METHODS: In 2002-2003 and 2005-2006, 20 Mycobacterium tuberculosis strains were sent by the WHO/Union Supranational Reference Laboratory of Rome to TB reference laboratories in Albania, Bahrain, Kosovo, Mozambique, Oman, Qatar and Turkey for external quality control (EQC). RESULTS: In 2002-2003, the specificity, sensitivity, efficiency, reproducibility and predictive values for resistance/susceptibility were ≥90% for streptomycin (SM), isoniazid (INH) and ethambutol (EMB). In 2005-2006, all statistical values were ≥96% for SM, INH, rifampicin and EMB. CONCLUSION: EQC improved the quality of M. tuberculosis DST in the participating countries. © 2008 The Union.