Delivery of polymorphonuclear cells (PMN) to sites of bacterial invasion is a critical step in host defense. Renal transplant patients have a defect in PMN delivery caused by glucocorticoid immunosuppressive therapy that leads to increased susceptibility to infection. Because inhibited granulocyte adherence is often associated with poor delivery, the effects of propranolol and of ascorbic acid were measured for both of these functions. Propranolol caused a short-lived increase in adherence and no change in delivery in normal volunteers, so it was not studied in transplant patients. Ascorbic acid also failed to affect adherence in normal controls, but increased depressed adherence in transplant patients from a mean value of 27.7% to 48.0% when given daily for 3-4 weeks. PMN delivery increased to normal following 3-6 weeks of ascorbic acid, 4 g/day in a similar group of patients with low adherence prior to treatment. Pretreatment delivery was 3.06 X 10(5) and rose to 1.18 X 10(6) PMN after treatment (P less than 0.02), with no change noted in graft function. Thus, ascorbic acid treatment may improve PMN host defense in renal transplant patients.