The C1q receptor (C1qR) on the human T lymphocyte line Jurkat cells was demonstrated and characterized. Cell-ELISA showed that Jurkat cells are able to bind exogenous C1q and recognized by the anti-C1qRantibody 112. FCM analysis indicated that the binding of FITC-C1q to Jurkat cells is blocked by an excess of unlabelled C1q.Quantitative binding studies with monomeric ¹²⁵I-C1q showed a specific, dose-dependent,saturable and reversible binding involving specific membrane receptors on Jurkat cells, Goldstein analysis and Hill plot of C1q binding showed 1.1×10⁶ binding sites per cell with an average affinity of 1.5×10⁷mol^-1 and a Hill number of 0.9643 at normal ionic strength(I=0 .15) and temperature(37℃). The experiment with the anti-Clq monoclonal antibody A₄，which recognizes the collagen-like region (CLR) of C1q, established that it is via its CLR that C1q binds to Jurkat cell receptors. Western blotting with the anti-C1qR antibody 112 revealed that the C1qR on Jurkat cells is a membrane protein of 70 ku.