The aim of this study was to estimate the cell mediated immunity (CMI) of uraemic patients, patients on regular dialysis (RDT) and patients who had received a transplant renal allograft (Post-Tx). The influence of the el'll on the outcome of renal transplantation (Tx) was also assessed. The following methods were used: (1) Dinitrochlorohenzene (DNCB) contact sensitivity skin test. The patients were sensitized by application to their forearm 2000 yg of DNCB. Two weeks later they were challenged with various doses of DNCB. This part of the test was improved by using DNCB applied on dry pads. The patients were classified into different categories according to the strength of their skin reaction to these challenge doses of DNCB. The test was repeated once or twice a year for RDT patients, and if a patient was transplanted it was repeated three weeks and six months after the Tx. (2) Old tuberculin (OT) skin test. This well known skin test was used and patients were also classified into different categories according to the strength of their reaction to OT. (3) Migration inhibition test was employed to assess the immunoreactivity of lymphocytes from patients on RDT who had been sensitized to DNCB skin test. As antigen a conjugate DNCB/RBC was used. (U) Levamisol was administered orally for an eight weeks period. DNCB and OT skin tests were done before initiation and after the cessation of treatment and the difference between the strength of these two tests before and after the trial was noted. It was found both by DNCB and OT skin test that patients on RDT had a profoundly depressed CMI. Post-Tx patients had an even further depression of this immunity. Using the DNCB skin test an unexpected difference betvreen the CMI of RDT patients dialysed at home and hospital was found, since the home dialysis patients had a much stronger CMI( P < 0.005.) There was no good, correlation between strength of DNCB skin test and when DNCB/KBC was used as antigen but there was a good correlation between MI and time passed since the last challenge of the patient with DNCB. Levamisole was shown to improve CICE of RDT but the number of patients was too small to permit general conclusions. A good correlation was found to exist between strength of DNCB skin test and OT skin test for RDT P <0.02 and Post-Tx patients P < 0.002. When the strength of the pre-Tx DNCB skin test was plotted against the six month. survival of the graft an excellent correlation was noticed P C<0.0025.) If the CM index was combined with the HLA mismatch between the donor and graft recipient the outcome of Tx could be predicted with reasonable accuracy. The immunological mechanisms of these results is discussed and the clinical importance of the findingsis evaluated.