Evidence has accumulated over the past three decades implicating plasma kininogens in numerous inflammatory processes. Delineation of the detailed biochemistry and, more recently, the molecular biology of the human kininogens has resulted in a deeper understanding of the structure-function correlations of the human kininogens. Studies of alterations of human kininogens in disease states have yielded information about the mechanisms of their involvement in inflammatory states. Here, Raul DeLa Cadena and Robert Colman summarize kininogen function in relation to structure and diagnostic and therapeutic potential.