First offered in 1963 at MIT (and the first under this title anywhere in the USA), the course 10.56 "Chemical Engineering in Medicine" was repeated in 1965 (with Clark Colton enrolled as a student), 1967, and 1969 (when Clark served with me as co-instructor). Thereafter Clark became sole professor in charge. Growing out of research on the rheology of human blood in the early 1960's , the focus of 10.56 increasingly sharpened and narrowed toward the membrane separations which underlie dialysis and oxygenation of blood- thus the "artificial kidney" and the " heart lung machine"-and toward delivery of therapeutic aerosols to the lung's alveolar membrane. We summarize the history of this evolution and the invaluable input and guidance of our medical and surgical collaborators.