OBJECTIVE: The accuracy of analytical results of blood and urine heavy metals came out to the main issue on occupational health from late eighties. The discrepancy of the results for same samples from different laboratories made the diagnosis for occupational diseases be unreliable. Therefore, a quality control program for analysis of samples taken from workplace had been introduced in Korea since 1992. This study aims to show the quality control program f'or analysis of blood and urine samples and its proficient rates from 1992 to 1999 and to know how they have been being used in occupational health. METHODS: The quality control program runs twice a year with mandatory items of blood lead and urine hippuvic acid and voluntary items of blood cadmium and manganese and urine mandellic acid and methyl hippuric acid. Participant laboratories are receiving three levels for each items and two out of three samples have to be qualified for being a proficient laboratory for the item. The acceptable range of blood lead and urine hippuric acid is +/-15% and that of the others is within 3 SD(standard deviation) from the reference values. RESULTS: The proficient rates of blood lead and urine hippuric acid was 89%, 90%, repectively, however those of the other voluntary items have been from 51% to 62%. The proficient rates of urine mercury and urine N-methylformamide(NMF), which are introduced since 1999, were very poor. Urine hippuric acid and blood lead were analyzed frequently for the purpose of biological monitoring conducting by special health examination organizations. Urine and blood manganese and urine metabolites of trichloroethylene, urine phenol, methylhippuric acid and cadmium were followed. CONCLUSIONS: In conclusion, the quality control program for biological monitoring has dramatically improve the ability of analysing blood and urine samples and eventually contributes to diagnose occupational diseases and to prevent occupational poisoning. However, some biological monitoring data, such as urine manganese, mercury and NMF, have been still reported from laboratories that were not accepted as a proficient laboratory.