Abstract Coagulation times in the lusteroid tubes used throughout this work were in the range of 14 to 28 minutes in a series of fifty normal controls. There is apparently no significant variation in coagulation time obtained when new or used tubes from the same batch were used. However, normal values must be determined for each new batch of tubes before they are put into use. The reliability of the test varies with the range of coagulation time. In the short range the experimental variation is very small; in the normal range it is somewhat greater. In nine (50 per cent) of the eighteen patients with arteriosclerosis obliterans studied, the coagulation times as measured by the lusteroid method were definitely less than for the normal subjects. No cases of acute occlusion were studied. Ten patients with clinically active or quiescent thromboangiitis obliterans with and without phlebitis were studied. In only three (30 per cent) was there any significant decrease of lusteroid coagulation time. These were two of the group of five patients with clinically active cases. The most pronounced shortening to less than normal of lusteroid coagulation time occurred in the patients with acute thrombophlebitis. It was noted in eight of the nine patients studied. Normal coagulation times were found in the two patients with subsiding thrombophlebitis. It is suggested that determination of the coagulation time in lusteroid tubes may be of value in indicating a tendency to thrombosis.