In this study, we have investigated whether lymphocyte growth from 196 liver transplant biopsies is correlated with the histologic diagnosis of graft rejection. One fragment of each biopsy was cultured in IL-2 to expand activated T cells, and the remainder of the biopsy was analyzed histologically. A significantly higher number of biopsies with rejection grew lymphocytes when compared to those biopsies showing no evidence of rejection (P = 0.009). Lower growth rates were observed with biopsies taken from patients on OKT3 therapy (12% vs. 29% from patients not on OKT3), so when the data were reanalyzed after omitting those biopsies we observed an even stronger correlation of growth with rejection (P = 0.001). In spite of the fact that hepatitis biopsies are also infiltrated by lymphoid cells, the frequency of lymphocyte growth (16%) was similar to that observed for the biopsies with no rejection or hepatitis (19%) and much lower than for biopsies with rejection (42%). Over all, 82% of the cultures tested were positive for donor PLT reactivity, suggesting that current culture conditions favor alloreactive lymphocyte proliferation. The size of the biopsy cultured was found to be an important factor in the propagation of biopsy-infiltrating lymphocytes. Only 25% of smaller (less than 3 mm long) biopsies with rejection grew lymphocytes compared to 91% of the large-sized biopsies (greater than 5 mm long). It is likely that culture techniques will need to be modified in order to successfully propagate infiltrating lymphocytes that recognize antigens other than alloantigens.