Tomato plants were grown in sand culture at 8 levels of K ranging from 0 to 10 meq per liter of nutrient solution. Fully ripened fruit were picked and rated internally and externally for abnormal pigmentation. Total carotenoids were analyzed and the extract fractionated into 3 groups: hydrocarbon, monohydroxy and polyhydroxy. The hydrocarbon fraction was further separated chromatographically into 6 individual pigments. Most of the carotenoids, lycopene in particular, generally increased with increasing K concn. A notable exception to this pattern was β-carotene which decreased with increasing K concn. Possible modes of action of K are discussed.