At a period when biology was largely descriptive, he collaborated with zoologists, botanists, organic chemists, and physicists conducting interdisciplinary studies, examining sensory biology (colour vision), behaviour, and biochemistry through experiments on organisms.
Among his major lines of investigation were the actions of genes in the development of organisms, particularly in the moth Ephestia kuehniella that he used as an experimental model.
He collaborated with the botanist Fritz von Wettstein, the physicist Richard Pohl, the chemists Gottwalt Fischer and Adolf Butenandt.
A major collaborator was his student Ernst Caspari who[2] was employed by Kühn until 1935 when the Nazi administration dismissed him for being Jewish.
[3] After the Nazi seizure of power, Kühn, together with Martin Staemmler and Friedrich Burgdörfer, authored the book Erbkunde, Rassenpflege, Bevölkerungspolitik.
Besides his research he was editor of the Zeitschrift für induktive Abstammungs- und Vererbungslehre and later also in charge of genetics at Der Biologe, a journal that was taken over by the SS's race science think tank.