During WW II, he served from 1943 to 1946 as an aviation physiologist in the U.S. Army and left with the rank of captain.
There he eventually became a full professor, director of student affairs, and assistant dean of graduate studies.
[3] During his tenure at UCSD he also served as associate dean for graduate studies, initiating the school’s very successful and competitive joint M.D./Ph.D.
He also served as associate dean for academic affairs, and as director of UCSD’s Health Professions Honors Program ...[3]His 135-page book The Cycling Female: Her Menstrual Rhythm was published in 1979 by W. H. Freeman and Company.
[5][6] Lein stayed in La Jolla and remained active in teaching and research for many years after his formal retirement.