Hepatitis C virus (HCV) is a leading indication for liver transplantation worldwide, but graft infection with HCV frequently leads to hepatic fibrosis. Acute cellular rejection (ACR) can be difficult to distinguish confidently from HCV, even with histology, but accurate diagnosis is critical because treatment of ACR may accelerate HCV-related graft injury. Immunohistochemistry was undertaken on 99 liver biopsies from 31 patients with HCV graft infection, 22 patients with ACR, and 11 patients with HCV infection and unexplained graft dysfunction to investigate whether lymphocyte expression of minichromosome maintenance protein-2 (Mcm-2), a marker of licensed cell cycle entry, assessed in a novel semiautomated system could distinguish between ACR and graft infection with HCV. The portal tract area was greater in ACR than in HCV graft infection (P = 0.027), but there was considerable overlap. However, both the number of Mcm-2-positive lymphocytes per portal tract and the number of Mcm-2-positive lymphocytes per millimeter squared of portal tract distinguished between ACR and HCV graft infection (P < 0.0001). A cutoff value of 107 positive cells per portal tract had a sensitivity of 81.8% and a specificity of 91.9% (positive predictive value of 66.67% and negative predictive value of 95.75%). Of 11 HCV-infected patients with an uncertain diagnosis, 7 were deemed ultimately to have HCV graft infection, and 4 had superimposed corticosteroid-responsive ACR. The number of Mcm-2-positive cells per portal tract and per millimeter squared of portal tract again distinguished clearly between the groups (P = 0.012). In conclusion, lymphocyte Mcm-2 expression is a useful adjunct to histology in differentiating between HCV graft infection and ACR. Patients with a low number of Mcm-2-positive portal tract lymphocytes are less likely to have ACR.