The role of aspiration cytology (AC) and the total corrected increment (TCI) in the diagnosis of hepatic rejection was assessed in 30 patients following 36 liver transplants. A total of 174 AC specimens were "blindly" evaluated. Patients underwent protocol AC twice weekly and when biochemical or clinical parameters suggested rejection. Hepatic rejection was only confirmed when clinical and biochemical changes were accompanied by positive histological diagnosis. In all, 103 specimens were matched against histology, the remainder assessed against retrospective clinical and biochemical diagnoses. There were 80 cytological diagnoses of rejection, confirmed in 69 specimens, and 94 diagnoses of no rejection, confirmed in 73 specimens. These figures give a sensitivity of 76.7%, a specificity of 86.9% and a positive predictive value of 86.3%. Overall, 39.7% of specimens taken more than 2 months after grafting proved to be incorrectly diagnosed. However, the accuracy was higher in 145 specimens taken within 8 weeks of transplantation, with a sensitivity of 81.3%, a specificity of 90%, a positive predictive value of 89.7% and an accuracy of 85.5%. Although histology remains the gold standard in the diagnosis of acute rejection after hepatic grafting, AC using a TCI with a positive predictive value of 86.3% may prove to be of value in monitoring liver transplant patients in the first 2 months after grafting.