A retrospective review of 375 consecutive orthotopic liver transplants was performed to determine the incidence and outcome of late rejection episodes ([LR] rejection occurring more than 6 months following transplant). A total of 31 episodes in 26 patients were identified. Eighteen of these episodes were associated with subtherapeutic levels of cyclosporine. Of these, 7 were due to noncompliance, 2 were due to biliary strictures, and 1 was due to malabsorption in a cystic fibrosis patient. All 31 episodes were treated initially with steroids, and 22 had a complete response, although one progressed to chronic rejection over a year later. Of the remaining 9, 1 received FK506 with a complete response, and 8 received OKT3. Of the 8 patients who received OKT3, 5 had a complete response, 1 received RS61443 following OKT3 and progressed to chronic rejection, and the remaining 2 received further steroids. Of these 2, 1 had a complete response following the steroids while the second was converted to FK506 with a complete response. Compared with 315 acute rejection episodes ([AR] occurring less than 6 months posttrans-plant), patients with late rejection episodes had an equivalent response to steroids (63.2% AR reversed vs. 71% LR reversed) but a lower response rate to OKT3 (91.5% AR reversed vs. 62.5% LR reversed). There was, therefore, a higher rate of persistent rejection (61% AR episodes vs. 15.4% LR episodes) but no increase in the incidence of chronic rejection (7% AR episodes vs. 7.7% LR episodes). We conclude that LR is a relatively common occurrence following liver transplant, which is most often associated with low cyclosporine levels. Many of these episodes are due to noncompliance, but biliary problems must also be investigated. The incidence of resistant rejection is higher in this group of patients but is not associated with a concurrent increase in chronic rejection.