Crustacean erythrophore concentrating hormone (CECH) was isolated from lobster (Homarus americanus) eyestalks by reverse phase high-performance liquid chromatography (rp-hplc). Putative lobster CECH fractions co-chromatographed with commercially available pure CECH on two independent rp-hplc systems, and were positive for activity by bioassay. CECH was detected in eyestalk, but not brain homogenates.