Curl described the isolation and proposed a tentative structure (I) of a carotenoid pigment, reticulataxanthin from the peel of tangerine fruit (Citrus reticulata). He deduced structure I through chemical and visible spectral investigations. The nature of the terminal group attached to the carbonyl was uncertain. This ambiguity invited further investigation, and we report herein a more complete structural study of reticulataxanthin. The pigment used in our study was extracted from the peel of the citrus hybrid, Minneola tangor (Citrus reticulata × Citrus sinensis) which proved to be a much richer source than tangerine. Column chromatography on magnesium oxide-Hyflo Supercel isolated and separated the pigment. Crystallization from peroxide-free ether-petroleum ether (b.p. 30-60°) furnished reticulataxanthin, C33H44O2. The infrared spectrum of the isolated pigment exhibited bands at 3450 (hydroxyl) and 1662 cm.-1 (conjugated carbonyl). The visible spectrum of reticulataxanthin indicated a decaenone chromophore similar to that of capsanthin (IV) and citranaxanthin (V). The n.m.r. spectrum revealed a singlet at τ 7.72 which can be assigned to an end-of-chain methyl group (γ to a carbonyl group). Additionally, no signal could be detected in the τ 0.3-0.6 region characteristic of aldehydic protons with αβ-unsaturation. The doublet at τ 2.50 (J = 16 c.P.s.) indicated that the double bond to which the vinyl proton β to the carbonyl is attached has the trans configuration. On treatment with aqueous alcoholic potassium hydroxide reticulataxanthin underwent a retroaldol cleavage to yield acetone and a compound identical with β-citraurin (III). On the basis of results described above, reticulataxanthin can be represented by structure II, but not I. This compound is a 3-hydroxy derivative of citranaxanthin.