Deficiency of kallikrein activity in plasma of patients with cystic fibrosis.

Total kallikrein activity and kallikrein activity inhibited by soybean trypsin inhibitor are significantly reduced in the plasma of patients with cystic fibrosis compared to age-matched controls. The level of the STI inhibited kallikrein activity in the plasma of heterozygotes was significantly different from that in either controls or affected children. However, the individual heterozygote could not be reliably identified in each case.