The subunit C1 of the carotenoid-binding protein, V600, of the chondrophore Velella velella has been purified and crystallized. The crystals, which were grown by the vapour-diffusion method from ammonium sulfate as the major precipitant, diffract beyond 3 A and show little radiation damage over long periods (greater than 100 h) on a Cu Kalpha rotating-anode X-ray source. The space group of the crystals is P212121 with cell dimensions a = 42.0, b = 80.9, c = 110. 6 A.