In many transplantation systems, the strength of the allograft response correlates with the magnitude of the in vitro mixed lymphocyte culture (MLC) reaction. Because this reaction requires 5 days, it has not been applicable to the prospective matching of cadaver renal allograft donors to the best available potential recipient. The pool primed lymphocyte test (pPLT) is a modification of the standard MLC assay; it measures primed lymphocyte responses after 24 to 30 hr of culture and these results correlate with data obtained after 5 days in the MLC. In this report, we analyze pPLT data from 69 recipients of cadaver renal transplants. No correlation between pPLT response and graft survival was found. Multiple factors were identified that influenced the magnitude of the pPLT response for these patients. Many uremic patients were unable to give any pPLT response, and some cadaver spleen cells were nonstimulatory. Nevertheless, the strength of pPLT responses by control individuals who did respond showed a positive correlation with their MLC responses. Thus, we feel the concept of using pPLT for prospective matching is sound; however, a number of technical variables make it impractical at present for routine transplant matching.