Despite the tension between the United States and the Soviet Union in the early 1920's, the Rockefeller Foundation and the Rockefeller Institute for Medical Research found ways to assist I.P. Pavlov. In addition to providing scientific literature and financial aid, these institutions and their officers rendered important moral support to the scientific career of Pavlov during his later years. In 1923, as a guest of the Rockefeller Institute, Pavlov visited American scientific laboratories. In 1924, he requested and received a number of books on physiology, and during the 1930's the Foundation helped him to acquire equipment for his Leningrad laboratory.