The pathogenesis of Limited Joint Mobility (LJM) in diabetes is unknown, but the abnormality is said to be associated with an increased incidence of microangiopathy. To examine the possibility that LJM may be a manifestation of microvascular disease, fibrinolysis and blood prostacyclin metabolites were measured in diabetic patients with and without LJM, and compared with patients who have systemic sclerosis (PSS). The concentrations of plasma fibrinogen (p less than 0.01) and Plasminogen Activator Activity (PAA) (p less than 0.02) were increased in both diabetic groups, compared with non-diabetic controls, and were of similar magnitude to the changes observed in PSS. Antithrombin III (AT III) activity was significantly lower in diabetic patients with LJM than in those without LJM, but not significantly different from controls. Prostacyclin concentrations were raised in PSS patients compared to controls (p less than 0.02) but were not raised in diabetic subjects. Thus abnormal fibrinolysis was demonstrated in diabetic patients compared to non-diabetic controls, and prostacyclin concentrations in diabetics were lower than in PSS patients. The diabetic patients with LJM had lower AT III activity than diabetics without LJM, but overall a convincing difference between the two groups of diabetics was not proven. No sure inferences could be drawn on the vascular aetiology of LJM, while the impaired prostacyclin activity might contribute to the development of diabetic microangiopathy.