Platelet function in vitro and in vivo and certain measurements of blood coagulability and fibrinolysis were examined in 12 patients with low tension glaucoma and the results were compared with those obtained in 12 normal subjects matched for age, race, and sex. The data obtained seem to indicate that patients with low tension glaucoma cannot be readily distinguished from individuals of similar age and sex not afflicted with this disorder by measuring these variables. Thus, a "hypercoagulable state," ie, a thrombotic tendency, does not appear to be of major importance in the pathogenesis of this disorder.