ON February 6, 1946, Nicholas D. Zelinskii, the most prominent chemist of the U.S.S.R., celebrated his eighty-fifth birthday. The following notes on his life are based on material sent by Prof. D. Rodionov. More than sixty years of original chemical work has made Zelinskii's name known and famous throughout the world. He was the first in Russia to emphasize the importance of the study of stereo-chemical problems, and he has made a personal contribution by his interesting investigations of stereoisomeric phenomena in the series of the saturated carbon compounds. In 1895 he began his classical syntheses of cycloparafnns, and discovered that naphtha of Russian origin is characterized by the presence of these compounds. This discovery opened a wide field to his numerous pupils and to other chemists, in the study of the natural naph-thenes. Since that time, Zelinskii has continued to interest himself in this subject, and after leaving the chair of organic chemistry in the University of Moscow, he was instrumental in establishing a new chair devoted to cognate studies. He has made many important investigations with collaborators on the pyrolysis of naphthenes to aromatic compounds, on naphthabenzination, on the synthetic preparation of high-grade petrol, on catalytic processes for the improvement of the iso-octane number and on many other similar topics.