Zur Kenntnis des Vitamins-A aus Fischtranen.

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."