Results are submitted of analysis of correlation between clinical efficacy of sulphanilamide drug preparations and endogenous reserves of insulin. As many as 102 patients with type II diabetes mellitus under varying efficacy of sulphanilamides, 15 patients with type I disease and 10 essentially healthy subjects were examined. Lack of effect from peroral therapy in case of secondary sulphanilamide resistance was found to be related to the insulin endogenous reserves diminution, which feature manifests itself by reduction of the body mass and therefore adipose tissue as well, in the human organism. The insulin-producing apparatus of beta-cells tends to get low in the glucose tolerance test, which fact is evidenced by lack of the blood glucose level control.