The purification of deoxycytidine kinase from human leucemic spleen reported here result in a pure protein of molecular weight 28K. The enzyme eluates during gel filtration as a dimer and the same enzyme phosphorylates both deoxycytidine, deoxyguanosine and deoxyadenosine, but with different Km and Vmax values. Our results are in agreement with earlier studies with partially purified calf thymus deoxycytidine, but clearly different from some studies on human deoxycytidine kinase.