Levels of total ascorbic acid and histamine in the peripheral venous blood of women during the third trimester of normal pregnancy have been estimated. The results suggest that ascorbic acid acts as a modulator to control the synthesis and/or release of histamine in the body. Low levels of ascorbic acid may be essential to stimulate the synthesis and/or release of histamine while in high concentrations it may function to inhibit the release and/or to enhance the breakdown of excessive quantities of histamine in the body. Substantial evidence is now available that histamine, perhaps its nascent variety, is essential for growth and repair processes in the body. It is possible that ascorbic acid in low concentrations acts to stimulate this variety of histamine while its high concentrations act to control the levels of histamine released from storage sites which contain preformed histamine.