In 1930 Karrer established the correct formula for carotene (the chief precursor of vitamin A), the first demonstration of the chemical structure of a vitamin. Shortly thereafter, he was able to determine the formula of vitamin A, and in 1931, he showed that vitamin A is structurally related to the carotenoids.

In 1937 Karrer received half of the Nobel Prize in Chemistry "for his investigations on carotenoids, flavins and vitamins A and B2." The other half was awarded to Walter Norman Haworth "for his investigations on carbohydrates and vitamin C." 

P. Karrer, H. Fritzsche, B. H. Ringier, and H. Salomon synthesized vitamin E (α-tocopherol).