The fractionation by solvents of the contents of the seeds of Annonamuricata (Annonaceae), guided by the toxic activity towards the brine shrimp larva and the KB cancer cells, has enabled us to isolate two new cytotoxic mono-tetrahydrofuran γ-lactones: corossolone 1 and corossolin 2. The structure of these two cytotoxic acetogenins was determined by analysis of the spectral data, NMR and MS in particular. The chemical correlation between 1 and 2 was established by the NaBH4 reduction of corossolone. 1 and 2 constitute the first examples of mono-tetrahydrofuran acetogenins with an unfunctionalized C-4. Keywords: Annonaceae, acetogenins, cytotoxicity, soursop, Annonamuricata.