The utility of bile cytology (BC) in the diagnosis of hepatic graft rejection was assessed in 21 liver trans plantations in 18 patients. A total of 307 BC specimens were studied; cell density and relative contribution of different cell types were monitored in 130 specimens. The findings in 62 fine-needle aspiration biopsies and 9 core needle biopsies (CNB) from the transplants were compared with those of the BC specimens.For the first 3–5 days after transplantation, BC specimens were cell-rich, containing degenerating cells and polymorphonuclear leukocytes. In uneventful cases, the cellularity of the specimens gradually decreased. Upon rejection, the number of cells increased, with a high percentage of PMN. Occasionally, blasts or macrophages were detected. After antirejection treatment, the cellularity of the specimens decreased. The analysis of the relationship between the findings of BC and FNAB showed that a high cell density was indicative of rejection. However, BC was not as sensitive to rejection as was FNAB. No clear-cut correlation was found between BC pattern and the degree of cell infiltration in portal triads as seen in CNB specimens. Our results indicate that serial bile cytology is valuable as an additional diagnostic method in monitoring hepatic graft rejection.