Dutch physician and pathologist whose demonstration that beriberi is caused by poor diet led to the discovery of vitamins (vitamin). Together with Sir Frederick Hopkins (Hopkins, Sir Frederick Gowland), he was awarded the 1929 Nobel Prize for Physiology or Medicine.

Eijkman received a medical degree from the University of Amsterdam (1883) and served as a medical officer in the Dutch East Indies (1883–85). He then worked with Robert Koch in Berlin on bacteriological research and in 1886 returned to Java to investigate the cause of beriberi. In 1888 Eijkman was appointed director of the research laboratory for pathological anatomy and bacteriology and of the Javanese Medical School in Batavia (now Jakarta). Eijkman sought a bacterial cause for beriberi. In 1890 polyneuritis broke out among his laboratory chickens. Noticing this disease's striking resemblance to the polyneuritis occurring in beriberi, he was eventually (1897) able to show that the condition was caused by feeding the fowl a diet of polished, rather than unpolished, rice.

Eijkman believed that the polyneuritis was caused by a toxic chemical agent, possibly originating from the action of intestinal microorganisms on boiled rice. He maintained this theory even after his successor in Batavia, Gerrit Grijns, demonstrated (1901) that the problem was a nutritional deficiency, later determined to be a lack of vitamin B₁ (thiamine). Eijkman returned to The Netherlands in 1896 to serve as a professor at the University of Utrecht (1898–1928).