A selected group of diabetic patients showed a statistically significant increase in levels of glycated proteins in the stratum corneum compared with a control group. The values of glycated proteins correlated with those of glycohaemoglobin (GHb), and in diabetic patients also with serum glucose concentrations. The values of glycated proteins (and GHb) exhibited a positive correlation with age both in a control group and in diabetic patients. The average values of glycated proteins (and GHb) were slightly higher in women than in men. Determination of glycated proteins levels of the stratum corneum can serve as a stable parameter for long-term monitoring of the course of non-enzymatic glycation in structural and connective tissues and thus also for the prognosis of the development of dermatological complications related to diabetes mellitus. In vitro incubation of stratum corneum proteins and keratin with glucose resulted in an increase of their glycation. The values of glycated proteins and glycated keratin increased proportionally to the glucose concentration and duration of incubation. Glucose binding to keratin and proteins of the insoluble stratum corneum fraction appeared to occur at practically the same rate, and it is a first-order reaction with regard to the glucose concentration. Water-soluble proteins of the stratum corneum undergo non-enzymatic glycation preferentially (on average, 83.4% of the total amount of glycated proteins is present in the soluble fraction), regardless of the initial content of glycated proteins in the sample. The content of glycated soluble proteins of a higher molecular weight significantly increased after 4 weeks of incubation with glucose.