Surgical biopsies from 21 patients with syndrome of organic hyperinsulinism were studied. Precise quantitative characteristics of "typical" and "atypical" beta-granules in tumor cells were obtained by means of quantitative and qualitative analysis. The criteria for establishing the tumor type (mono- or polyhormonal) and the degree of hormonal activity are established. The validity of these criteria is confirmed by positive correlation between the secretory activity of the tumor and insulin level in the patient's blood.