Castilleja rhexifolia was found to contain senecionine and its N-oxide as major alkaloids of the stems and leaves, while a new pyridine monoterpene alkaloid (rhexifoline) was the major alkaloid of the blossoms and seeds. A purported hybrid of C. rhexifolia with Castilleja miniata was found to contain sarracine and three new alkaloids, (7-angelylplatynecine, 9-angelylplatynecine, and its N-oxide) in stems and leaves. A trace of senecionine was found. The major alkaloid of the whole plant, but particularly concentrated in the seeds, was rhexifoline. Deoxyrhexifoline was also identified from the seeds. Both larvae and adults of the plume moth (Platyptilia pica, Lepidoptera), which is hosted by C. rhexifolia, contain alkaloids. An extract of adult moths was shown by gc-ms to contain rhexifoline. © 1984, American Chemical Society. All rights reserved.