Abstract The HM r and LM r molecular forms of kininogen were found to occur in normal distribution in plasma from a patient with severe haemophilia A. Present findings indicate that lack of Factor VIII does not influence, the normal content and distribution of immunoreactive kininogens determined by single radial immunodiffusion and radioimmunoassay. The partially purified HM r and LM r kininogens were antigenically identical with the kininogens in normal human plasma determined using the monospecific antisera raised in rabbits against purified kininogen antigens. Low kallikrein activity on H-D-Pro-Phe-Arg-pNA in the haemophilic plasma was apparently due to preparative procedures. This concept is supported by the normal binding ratio of trypsin to pure α 2-macroglobulin isolated from the haemophilic plasma.