Assess the relationship between Tacrolimus (TAC) whole blood trough level (BT0L), lymphocyte trough level (LT0L) and the degree of immune responsiveness reflected by the total lymphocyte count (LC) in stable kidney transplant patients.: A total of 208 blood samples were obtained from 27 patients at different TAC dosages during the first 6 months post-transplantation. BT0L, LT0L and total LC were determined simultaneously. BT0L and LT0L were compared among each other and according to TAC dosage and the relationships between these three parameters (BT0L, LT0L and dose) and the total LC were analysed. Results: Significant inter-patients variations were observed for both BT0L and LT0L within each TAC dosage responsible for the poor relationship between BT0L (R2=0.083), LT0L (R2=0.15) and TAC dosage, respectively. This has resulted in the lack of correlation between BT0L and LT0L (R2=0.029). Similarly, a substantial difference in the total LC was observed among patients when compared in relation to their TAC dosage (R2=0.04) and it failed to correlate with BT0L (R2=0.016). In contrast, LT0L strongly correlated (R2=0.76) with the total LC in a exponential manner. Our results clearly demonstrate a poor relationship between TAC BT0L and both TAC lymphocyte content (LT0L) and immune responsiveness. Given its strong correlation with the LC, LT0L may offer a new alternative for TAC therapy monitoring in renal transplantation.