A detailed audit was done of eight of the twenty-nine transplant centres serving the UK and Ireland. These 8 centres account for one-third of the total renal transplant operations in these two countries. Information was obtained from each centre by means of a comprehensive questionnaire, a 1 1/2 day visit by the three authors, and an analysis of 50 consecutive first cadaver transplants. The 8 centres were chosen in the knowledge that 4 had high and 4 had low 3-month graft-survival rates. Our audit confirmed a centre effect, with a range in 1-year patient survival of from 82% to 96% and of first cadaver graft survival of from 54% to 82%. The two main factors affecting success rate were the rate of irreversible acute rejection and death with a functioning kidney. Our investigations suggested that the centre variation in acute rejection was influenced by blood transfusion and the variation in mortality by steroid dose and recipient age. Careful and well-organised clinical management cannot be easily quantified but was thought to have an important influence. Widespread adoption of pre-transplant blood transfusion and increasing use of cyclosporin will probably contribute to the further lessening of the centre effect which has already been observed over the past few years.