The alkaloid content of the poppy Argemone gracilenta Greene has been investigated. Of the total alkaloid content, over 90% was argemonine. Other known alkaloids found were (+)-laudanidine, (-)-munitagine, muramine, protopine, (+)-reticuline, and (-)-platycerine. The structure of (-)-platycerine was unequivocally established. New natural alkaloids isolated were (-)-argemonine N-oxide, (-)-argemonine methohydroxide, and (-)-isonorargemonine. © 1969, American Chemical Society. All rights reserved.