 Shortly after the war, in 1948 Gajewski was one of the few Polish biologists who opposed the official "new biology", lysenkoism -- a pseudoscientific theory of genetics proposed by the Soviet agronomist Trofim Lysenko.Consequently, during the Stalinist period Gajewski was not allowed any contact with students; however, he was permitted to continue his scientific work.In 1956, with the end of Stalinism and the diminishing importance of lysenkoism, Gajewski was allowed to hold a position of lecturer at the Uniwersytet Warszawski, where two years later, the first Polish department of genetics was established under his leadership.