Semicarbazide-sensitive amine oxidase (SSAO) has been suggested to be involved in the development of vascular endothelial damage. The source of the soluble form of SSAO found in the blood serum is unknown. However, it has been speculated that it is secreted from cells within the vascular wall where high activity of the enzyme is found. Altered SSAO activity has been reported in atherosclerotic plaques of the human aorta. Stroke is a manifestation of long-term atherosclerotic disease, and in this study, plasma SSAO activities were estimated in 42 patients with cerebral thrombosis and 26 patients with cerebral embolism, and compared to two control groups of 45 individuals in total. No statistically significant differences were found between the patient groups and controls regarding plasma SSAO activity, suggesting that changes in the soluble form of SSAO found in the circulation do not play a major role in this type of acute cerebrovascular event. Furthermore, it does not seem likely that the involvement of vascular tissue occurring in stroke results in release of the enzyme into the circulation. Nevertheless, further studies on tissue-bound SSAO in cerebral vessels would be of great interest.