On the Thai-Myanmar border, where multidrug resistance to anti-malaria medications is a major problem, a quality control program for diagnostic laboratories has been set up. This study examines the "passive" screening performed in 10 laboratories. Monthly evaluation of the quality of thick and thin smear practice, Giemsa staining and microscopy took place during the year 1994. Considering the general context and the methodology applied, the evaluation of performance and strategy of the malaria diagnostic test showed satisfactory results for all 10 laboratories. Performance of technics = 64% (62-66) to 96% (95-97); Sensitivity = 92.6 (91.5-95.5) to 96.6% (95.8-99.0); Specificity = 93.5% (91.4-95.5) to 98.3% (97.6-99.0); Predictive Positive Value = 92.0% (90.9-93.1) to 98.3% (97.6-99.0); Predictive Negative Value = 94.3% (93.0-95.6) to 98.5% (98.0-99.0). The study underlines the importance of a reliable quality control method for microscopy diagnosis of malaria in hyperendemic areas, with Plasmodium falciparum as the main species. A high level of input from the international laboratory technician, performing training, follow-up and evaluation was required. The need for adequate training of national technicians and supervisors, especially regarding long-term sustainability, is stressed. The type of program presented can be used as a model for similar projects in developing countries.