Derivatives of 7-substituted-8-amino-3-methylxanthines is a promising group of substances for synthesis and pharmacological screening in order to create diuretics, for pharmacological correction of the kidneys, on their basis. The acute toxicity and diuretic activity dependence on the chemical structure for the first synthesized 7-substituted-8-amino-3-methylxanthines in experiments on rats was investigated. 3-Methyl-7-(2-hydroxy-3-p-methoxyphenoxy)propyl-8-(2-furyl)methylaminoxanthine, increases urine excretion at 201.3% and is higher in the diuretic effect comparing to hydrochlorothiazide up to 111.3%.