The Rhamnus plant genus has 10 species growing in Croatia. Frangulae cortex pharmaceutical preparation from Rhamnus frangula (= Frangula alnus) contains a mixture of anthracene derivatives, flavonoids, tannins, and peptide alkaloids. This herbal drug is used as a laxative. Bark from 9 Rhamnus species (R. alaternus, R. cathartica, R. fallax, R. frangula, R. intermedia, R. orbiculata, R. pumila, R. rupestris [= Frangula rupestris], R. saxatilis) was collected in several Croatian locations and analyzed by thin-layer chromatog. (TLC) in comparison with the com. Frangulae cortex preparation The TLC used Silicagel 60 F254 20x20 cm plates, water/methanol/Et acetate (13:17:100) eluent, and detection with 5% KOH in 50% ethanol. The TLC separation of anthracene derivatives indicated the presence of glucofrangulins (A and B), rhein, barbaloin, frangulins (A and B), and danthrone only in R. frangula and R. fallax, while R. alaternus and R. pumila contained danthrone.