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The study was designed to assess routine SMEAR MICROSCOPY in 285 tuberculosis (TB) public health laboratories of Iran. Over one year period (1999), the information regarding infrastructure, specimen processing (smearing, staining, smear reading), and safety points of TB laboratories were collected. Thereafter, in two consecutive years (2000 & 2001), the accuracy of smear reading was investigated by sending a set of 6 blinded slides to each laboratory. In total, 1710 (X2) slides were prepared, of which 855 were positive (having varying degree of positivity), and 855 were negative. We found that 68.4% of TB laboratories were using commercially prepared staining kits of inferior quality and 72% of TB technicians examined each slide for less than 7 minutes whereas the recommended standard time is 15-20 minutes. The results of blinded smear reading in the first round demonstrated 71% of accuracy. However, after 3 days of SMEAR MICROSCOPY training for personnel in 60 poorly performing laboratories, we observed a substantial improvement in the quality of microscopy. The number of false positive reports dropped from 20 to 0 (p< 0.05), and the number of negative reports declined from 40 to 5 (p< 0.05). Overall, out of 237 participating laboratories in the second round, 217 (91%) laboratories could correctly detect positive and negative smears. This study demonstrates the importance of QUALITY CONTROL and correct performance of SMEAR MICROSCOPY. It also emphasizes the need for implementing strict and ongoing QUALITY CONTROL for all laboratory procedures.