Plants from Suriname (South-America) and several Annona species, including A. muricata, A. ckerimolia, A. montana and A. glabra were screened for 5-HT(1A) receptor binding activity by ligand-binding-studies (LBS). Crude extracts of all Annona species and from Hibiscus bifurcatus, Irlbarchia purpurascens and Scoparia dulcis showed high activity. The isoquinoline alkaloids asimilobine (1), nornuciferine (2), and annonaine (3) were isolated as the active principles from the fruit of Annona muricata. These results may partially explain the use of Hibiscus bifurcatus and Annona muricata in traditional medicine in Suriname.