German microbiologist
Karl Bernhard Lehmann (27 September 1858 – 28 January 1940) was a German hygienist and bacteriologist born in Zurich. He was a brother to publisher Julius Friedrich Lehmann (1864–1935).
Lehmann studied medicine at the University of Munich, where one of his instructors was Max von Pettenkofer (1818–1901). In 1886, he received his habilitation, and from 1894 to 1932 was a full professor of hygiene at the University of Würzburg (emeritus 1932).
He is remembered for pioneer toxicological research he performed with Ferdinand Flury (1877–1947), of which the exposure limits of various substances encountered in the workplace were tested and defined. Their research formed a basis of what would later be known as MAK values ("Maximale Arbeitsplatz-Konzentration") in Germany. 
In the field of microbiology he was co-author with Rudolf Otto Neumann (1868–1952) of "Atlas und Grundriss der Bakteriologie und Lehrbuch der speziellen bakteriologischen Diagnostik", a manual/textbook which over several editions described a number of new bacterial species.
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