The science suffered a severe loss with the sudden death in November 2, 1991, of and outstanding physiologist Academician Alexander Mikhaĭlovich Ugolev at the age of 66. All life of this man was devoted to the development of the national science. It was the aim and meaning of his life, he has contributed to scientific progress in every possible way. The major scientific interests of A. M. Ugolev were focused on the basic and applied areas of food assimilation, including the physiology of nutrition and digestion. The works of the scientist in this field of knowledge were world-wide recognized. During his scientific activity Dr. Ugolev conducted a number of brilliant studies which remained unforgettable trace in physiology and for ever will be a part of golden fund of science. This was promoted by a unique combination of his illustrious abilities of physiologist and general biologist as well as evolutionist with the gift of experimenter and excellent surgeon. His experimental skill can serve and example of an elegant combination of bold intentions and their masterly realizations. But the most remarkable and world-wide recognized discovery of the scientist was that of membrane digestion--previously unknown mechanism of food assimilation. Just this basic discovery is emphasized in the review devoted to the memory of unforgettable master. The fragmentariness of material depends on a desire to present concisely the major characteristics of membrane digestion.