Carl Jakob Adolf Christian Gerhardt (there are several variations regarding the arrangement of his 3 middle names); (5 May 1833 - 22 July 1902) was a German internist born in Speyer.
He studied medicine at the University of Würzburg, earning his doctorate in 1856. Subsequently he was an assistant to Heinrich von Bamberger (1822–1888) and Franz von Rinecker (1811–1883) in Würzburg, and worked under Wilhelm Griesinger (1817–1868) in Tübingen.
In 1860 he received his habiltation in Würzburg, and during the following year was appointed professor of medicine and head of the department of internal medicine at the University of Jena. In 1872 he returned to the University of Würzburg to fulfill similar duties. In 1885 he was successor to pathologist Friedrich Theodor von Frerichs (1819–1885) at the Charité in Berlin, where he established the second internal medicine clinic. At Berlin, one of his assistants was immunologist Paul Ehrlich (1854–1915). His son, Dietrich Gerhardt (1866–1921) was also a noted physician.
Gerhardt is remembered for his pioneer work in pediatrics, being the editor of an influential textbook on pediatrics called Handbuch der Kinderkrankheiten. He also performed important research involving auscultation & percussion, and conducted investigations of diabetes. Gerhardt used iron chloride to detect acetone in diabetes (Gerhardt's reaction). In 1892 he provided an early description of erythromelalgia, which was once referred to as "Gerhardt’s disease".