1. Astaxanthin ester, astaxanthin, and astacin were found as major pigments in the exoskeleton of crayfish.
2. Astaxanthin, which was the prosthetic group of carotenoproteins, was found in comparatively larger quantities in the exoskeleton of cepharothorax and abdomen & tail than in those of chelae and legs.
3. A remarkable difference of carotenoid composition, however, was not found between the red and the blue chela exoskeletons.
4. The blue in the exoskeleton may depend on bluish carotenoproteins, and on the carotenoproteins replaced by unbound-carotenoids deposited as the animal older. The unbound-carotenoids seemed to be in relation with the basal pigmentation of the reddish exoskeleton.