A flotation method for preparing synaptosomes, previously developed for work with squid nervous tissue, has now been successfully applied to the ventral nerve cord of lobster. Perhaps due to the greater content of connective tissue, homogenization of the lobster nerve cord was more difficult than with squid optic lobes and the yield of synaptosomes was lower. The synaptosomes fraction showed a 3.8-fold enrichment of bound acetylcholine relative to the homogenate and was almost 10 times richer in acetylcholine than a guinea pig cerebral cortical synaptosome fraction. The lobster synaptosomes accumulated choline rapidly when incubated at room temperature in sea water, and showed a high degree of occlusion of lactate dehydrogenase, thus confirming that they are sealed structures. The lobster can thus be added to the wide range of species from whose nervous systems synaptosomes can be isolated, and merits further study as a possibly rich source of cholinergic synaptosomes.