Seven crystalline alkaloids have been isolated and identified from extracts of a Mexican "peyote" cactus, Dolichothele longimamma (DC.) Br. and R. Five of these are new alkaloids: N-methyl-ß-hydroxy-4-methoxy-ß-phenethylamine (longimammine or 4-O-methylsynephrine), 6-hydroxy-2-methyl-1,2,3,4-tetrahydroisoquinoline (longimammosine), 8-hydroxy-2-methyl-1,2,3,4-tetrahydroisoquinoline (longimammidine), 6-methoxy-1,2,3,4-tetrahydroisoquinoline (longimammatine), and 4,8-dihydroxy-2-methyl-1,2,3,4-tetrahydroisoquinoline (longimammamine). Although these compounds have all previously been synthesized, a new and convenient route is described for the syntheses of longimammidine and longimammosine. The known cactus alkaloids, (-)-normacromerine and (±)-synephrine, were also found in this species.