Transplantation is a widely recognized method of treatment at the terminal stages of many renal, cardiac, hepatic and pulmonary diseases. Despite considerable advances in that field, graft rejection is still an important clinical problem. The reaction of the graft recipient to an organ presenting foreign antigens is dependent on complex immune mechanisms, involving both acquired and congenital immune responses. In most general terms, cellular and humoral immunity can be distinguished. The kidneys and the heart are the organs whose acute humoral rejection has been thoroughly investigated and defined, and the role of C4d and C3d fragments of the complement system has been confirmed by numerous studies. The studies concerning C4d and C3d expression in patients with acute humoral lung and liver rejection conducted to date have given contradictory results. Some of them confirm, while others fail to confirm, the correlation between their increased expression and AHR. From the practical point of view, C4d and C3d could be used in liver transplantology for differential diagnostics of acute graft rejection and recurrence of HCV infection. A few preliminary studies suggest the usefulness of these markers in the diagnostics of AMR and differentiation between both liver pathologies. There are only single reports concerning the role of C4d complement fragment in the diagnostics of acute rejection with a humoral component in case of small intestine grafts, as well as complex ones such as the hands and face, and their results suggests that these complement fragments are not important markers of acute rejection of these organs.