A series of immunological parameters were used to follow 41 necrokidney transplantations, in an investigation of the correlation between these parameters and graft function, rejection and graft survival. The results showed that patient and graft survival were not dependent on the occurrence of rejection, but were related to decrease in lumphocyte counts and IgG in the initial post-operative period. Initial decreases in lymphocyte count, IgG, IgA and IgM were found. There was no correlation between initial donor-recipient MLC response and graft survial. In the post-operative period there were falls in PHA, PWM and PPD responses and in numbers of cells forming T and B rosettes, but no change in MLC response. Lowest measured values for lymphocytes and IgC tended to occur just before rejection, but there was no depression of the measured in vitro immune responses at this time. However, MLC and PHA responses were depressed during rejection. When these results are compared with similar results in the literature, which shows a lack of convincing correlation between existing immunological tests and the course of transplantation, it is concluded that the immunological tests available today are unsatisfactory for use in monitoring immune response as an aid to the adquate immunosuppression of receipients.