The relative proportions of CD5, CD4, CD8, SBU-T19 and surface immunoglobulin (sIg)-positive lymphocytes in normal sheep livers were determined by flow cytometry analysis of isolated liver leucocytes and compared to lymphocyte subpopulations found in peripheral blood and hepatic lymph nodes. In contrast to the blood, very low numbers of SBU-T19+ cells were found in both the liver and hepatic lymph nodes. The ratio of helper versus suppressor/cytotoxic T cells in the liver was less than 1, which was much lower than in blood or hepatic lymph nodes. A large proportion of liver lymphocytes were characterized by a low intensity staining for the CD8 antigen (CD8L). Two-colour flow cytometry analysis revealed that the CD8L cells were negative for the CD5 pan T-cell marker. It is suggested that these CD8LCD5- cells are natural killer (NK) cells similar to those found in the gut. An influx of CD8LCD5- cells was observed in leucocyte-infiltrated liver lesions at later stages of a rejection response to the cestode Taenia hydatigena.