A comprehensive study of renal function in patients with early forms of syphilis revealed a decrease in tubular secretion and a decrease in effective renal plasma flow in one third of the examined. The possibility of preferential damage to one of the kidneys was established in half of the patients. The therapy in general had a normalizing effect on kidney function. Temporarily decreased tubular secretion and effective renal plasma flow after pyrotherapy normalized or significantly improved by the end of treatment in comparison with the baseline data.