1. 1. The pigments of the spider mite Tetranychus cinnabarinus and of the bean leaves the mites are feeding upon were investigated. 2. 2. Leaves of bean plants (Phaseolus vulgaris L.) were found to contain α-carotene, β-carotene, cryptoxanthin, lutein, lutein-5,6-epoxide, violaxanthin and neoxanthin. 3. 3. Besides chlorophylls a and b two chlorophyll derivatives thirteen carotenoids were isolated and identified from T. cinnabarinus. 4. 4. α-Carotene, β-carotene, lutein, lutein-5,6-epoxide, violaxanthin and neoxanthin are plant derived carotenoids found in extracts of T. cinnabarinus. 5. 5. From saponified extract of this spider mite three major keto-carotenoids were identified: 3,4-diketo-β-carotene, 3,4,4′-triketo-β-carotene and astacene. In the organism they are present in the form of esters of 3-hydroxy-4-keto--gb-carotene, 3-hydroxy-4,4′-diketo-β-carotene and astaxanthin respectively. 6. 6. Very small amounts of four other carotenoids were found: echinenone, isocryptoxanthin, a not identified monoepoxide and a diepoxide, possibly 5,6,5′,6′-diepoxy-β-carotene. 7. 7. A tentative scheme for the metabolism of carotenoids in T. cinnabarinus is given.