Abstract: Seiologic and pathologic studies of 24 cases with erythema chronicum migrans （ECM） were reported. The serum anti-Borrelia burgdorferi（BB） antibody was measured by ELISA in 24 cases with ECM. The Binding Indexes of IgM and IgG anti-BB antibodies were significantl increased in 20（83%）and 11（45%） out of the 24 cases with ECM, respectively （p＜0.01）. The histologic findings of skin biopsy specimens from ECM lesion in 7 cases consisted of perivascular and interstitial infiltrate of lymphocytes, plasma cells and/or eosinophils, mast cells. These studies showed that the determination of anti-BB antibody is sensitive and specific for diagnosing early Lyme disease.