Five new sesquiterpene lactones (1,2,4,5 and 6) have been isolated from the hexane extract of the heartwood of Callitris columellaris, F. Muell. (syn. C. glauca). In addition, a sixth lactone (3), previously reported' as a synthetic compound, has been established as a natural product from the same source. Callitrin (1), callitrisin (2) and the germacranolide (3) were extracted into aqueous silver nitrate solution* from the neutral hexane fraction. Treatment of the silver nitrate solution with excess ammonia liberated an oil from which the crystalline lactones (1), (2) and (3) were isolated by chromatography over alumina containing ca 10% silver nitrate. Dihydrocallitrisin (4) and the guaianolides dihydrocolumellarin (5) and columellarin (6) were isolated by chromatography of the silver nitrate insoluble portion of the extract using "Merck" prepacked silica gel columns.