The first phase of the intrinsic coagulation system was studied in twenty‐six diabetic outpatients. The parameters tested were kallicrein, prekallicrein, factor XI and factor XII activities. Kallicrein and factor XI showed significantly elevated activities as compared with a normal control group (P<0·05 and <0·001, respectively). Factor XI and factor XII levels were higher in non‐insulin dependent than in insulin dependent diabetics. We found that the kallicreinprekallicrein system was activated in our diabetic patients and that such activation could probably be secondary to lesions of the vascular endothelium present in long‐term diabetics. No correlation was found between glycaemia and activity levels of this system. Our data represent another demonstration of the existence of a hypercoagulable state in diabetes mellitus.