Deprotonation of the carotenoid radical cation (Car(.+)) in CH2Cl2 was studied by electrochemistry, optical, MALDI-TOF, and EPR spectroscopy. Water enhances deprotonation of the carotenoid radical cation. The formation of a didehydrodimer (#Car)(2) (#Car: Car with one less proton) was confirmed by the above techniques. The structure of the dimer is proposed on the basis of semiempirical calculations, optical, and EPR studies.