Abstract: Determination of serum anti-Borrelia burgdorferi antibody（A BB Ab） is a diagnostic aid useful in Lyme disease. Borrelia burgdorferi（BB） obtained from American Type culture was grown in modified Kelly medium. The spirochaetes were incubated at 35℃ for 5-7 days and the organisms were harvested by centrifugation and sonicated by sonicator. The sonicate was centrifuged. The supernatant was used as the antigen. The serum anti-BB Ab of 99 normal controls was measured by ELISA. 2SD above the nomal mean values of Binding Index （BI） of IgM and IgG anti-BB Ab were set as the upper limit for nomal value. The normal BI of IgM was 2.51 and that of IgG 2.85. The results were fairly stable. The coefficient of variation was less than 10 per cent.