Tuberculosis is a common complication after kidney transplantation and is not easy to diagnose in the early stage. Determination of serum anti-PPD-IgG level in our laboratory indicated that it was positive in patients with active tuberculosis. The mean time (20.5 days) required to diagnose with this method was obviously shorter than that (66.8 days) required with bacteriology, pathology or imaging. There was no obvious rise in the serum level of anti-PPD-IgG in fever caused by other infections and rejection and the serum anti-PPD-IgG level in patients with tuberculosis controlled returned to normal. It is shown that determination of serum specific antibody is a better index for early diagnosis of tuberculosis complicating kidney transplantation.