Nine Brazilian Amaryllidaceae species were studied for their alkaloid composition and acetylcholinesterase (AChE) inhibitory activity via GC–MS and a modified Ellman assay, respectively. A total of thirty-six alkaloids were identified in these plants, of which Hippeastrum papilio and H. glau-cescens exhibited the highest galanthamine content and the best IC 50 values against AChE. Furthermore, Hippeastrum vittatum and Rhodophiala bifida also showed notable AChE inhibitory effects. X-ray crystallographic data for four galanthamine-type compounds revealed significant differences in the orientation of the N-methyl group, which are shown to be related to AChE inhibition. Keywords Galanthamine Á GC–MS Á Hippeastrum Á Sanguinine Á X-ray crystallography