The cytological patterns in bile were compared with the histological findings in concomitant specimens from liver transplants. In cases where cytology showed a moderate (n = 10) or high cell density (n = 8), histology demonstrated rejection in 14 of 18 specimens and cholangitis in 4. When the cell density was low (n = 22), histology was nearly normal in 3 specimens and showed cholangitis in 9, while rejection was observed in 10 specimens. Cell density in bile did not correlate quantitatively with the severity of cellular infiltration in the portal triads or with the percentage of bile ducts attacked by inflammatory cells. The results of the present study support our hypothesis that an increased concentration of cells in bile is indicative of liver transplant rejection (sensitivity 58%), while normal cytology does not rule out the possibility of rejection (specificity 75%).