The aim of this study is to evaluate the correlation between the 2 methods used to monitor thymoglobulin therapy: the total lymphocyte count and the number of T cells. We have performed daily collections of peripherical blood samples from 24 renal grafts, recipients who were receiving thymoglobulin, including 14 cases for induction and 10 for acute rejection. Absolute lymphocyte and T-cell counts were measured in the 298 samples after administration of a dose of 1.25 mg/kg/d. The dose was omitted if the T-cell count had decreased to <10 cells/microL. The theoretical total lymphocyte count considered to omit dose was <100 cells/microL. A total of 137 doses were given according to T-cell count. We performed the comparison in 3 steps. First, we correlated values in the daily samples; second, we examined samples as a whole and third, assessed the percentage of discrepancy between the omission of the daily dose according to each method. There was a poor correlation between the methods according to sets of daily samples or the sets as a whole. The rate of discrepancy was 66%, including 121 of 216 decisions (P<.001). In conclusion, the results of the 2 methods of monitoring thymoglobulin therapy are different, and the total administered dose depends on the method used.