The alkaloid content was determined, mainly by GCMS, for three rare western United States species of the Papaveraceae: Arctomecon californica, A. humilis and A. merriamii. Allocryptopine and protopine were major alkaloids in all species, along with lesser quantities of a new alkaloid, 12-methoxyallocryptopine. Eleven other alkaloids, especially benzophenanthridines, were detected in minor amounts. The pattern of alkaloid structures in Arctomecon, one of the few remaining genera of the Papaveraceae left to be studied in detail, is briefly discussed. © 1990.