Free (FA) and total (TA) activities of cathepsin D in serum of 86 patients in the acute period of ischemic stroke (IS) were studied. It was established that in patients with IS FA and TA of cathepsin D increases. The activity of cathepsin D depends on the patient`s age and stroke severety. In 45-60 year-old patients on the 1st day of IS we revealed significantly greater TA and FA of cathepsin D compared with patients older than 60. On the 7th day FA of cathepsin D in 45-60 year-old patients was significantly lower than in patients older than 60 and correlated with the patient`s age. The lowest TA and FA of cathepsin D on the 1st day were found in the patients with mild IS, the highest – in the patients with moderate stroke. In patients with mild and moderate IS on the 7th day was observed reduced FA of cathepsin D while in the patients with severe IS - its increase.