Peripentadenine, the principal alkaloid of the elaeocarpaceous plant Peripentadenia mearsii, has been shown by spectroscopy, degradation, and synthesis to be N{3[2(2-hydroxy-6-methylbenzoylmethyl)pyrrolidin-1-yl]propyl}hexanamide (1). Peripentadenia mearsii (C. T. White) L. S. Smith is a tree growing in rain forests of north Queensland. The genus concerned is monotypic and belongs to the family Elaeocarpaceae, from which a range of indolizidine (1) and indole (2) alkaloids has been reported. A previous examination of P. mearsii for alkaloids yielded tropane bases (3), but this finding could not be repeated subsequently, and the tropanes had evidently come from some other plant, so far unidentified (4). The present study has been carried out on authentic material that has been checked against herbarium voucher specimens. In addition to the major base peripentadenine (1), which is described here, a number of others have been isolated from leaf and bark extracts; the minor alkaloids will be treated in a subsequent report.