Rosalyn Yalow developed radioimmunoassay and won the 1977 Nobel Prize in Physiology or Medicine.
Radioimmunoassay uses radioactive tracers and antibodies to measure tiny concentrations of substances in blood and other biological samples. Yalow developed the technique with Solomon Berson, initially to study insulin and other hormones.
The method transformed endocrinology because it allowed researchers and clinicians to detect hormones at extremely low levels. It was later applied to substances including vitamins, drugs and viral antigens, making it valuable in diagnosis and biomedical research.
Yalow shared the 1977 prize with Roger Guillemin and Andrew Schally. Berson had died before the award and therefore could not share the Nobel Prize, although his central contribution is widely acknowledged.