In 41 consecutive living and cadaver donor renal transplant recipients, immunological monitoring was performed 2--3 times a week for the first two post-transplant months. Monitoring consisted of: 1) Circulating T and B cell levels (E-EAC Rosette assay) 2) T cell reactivity (PHA-Con A) 3) LMC and ADCC reactivity Rejection was diagnosed by standard techniques including radioisotope renal scans and biopsy in some cases. Immunosuppression consisted of prednisone, imuran, cyclophosphamide and horse ALG. In 32 rejection episodes in the first two months, 22 (68%) were associated with a rise in T cell levels. Rejection activity also correlated with an augmented PHA mitogenesis count of 20 +/- 5%. There was no positive correlation between Con A mitogenesis and rejection. There was also no correlation between rejection and circulating B cell levels. There was no significant correlation between a positive ADCC and graft rejection. Futhermore a positive ADCC in association with a negative LMC resulted in excellent long-term graft function. In conclusion, an excellent correlation of levels of circulating T cells and T cell reactivity with early in vivo rejection was shown.