The extract SG 291 (Talso, Talso uno) from the fruits of Sabal serrulata (syn.: Serenoa repens) prepared by supercritical fluid extraction with carbon dioxide is used for the treatment of benign prostatic hyperplasia (BPH) and non bacterial prostatitis. In the present work, the Sabal extract SG 291 was analyzed by gas chromatography and investigated for its inhibitory influence on the biosynthesis of inflammatory arachidonic acid metabolites. The extract SG 291 was found in vitro to be a dual inhibitor of the cyclooxygenase (IC50-value: 28.1 micrograms/ml) and 5-lipoxygenase pathway (IC50-value: 18.0 micrograms/ml). By alkaline hydrolysis, ether extraction and preparative thin layer chromatography the extract SG 291 was separated in three fractions containing acid lipophilic compounds (A), fatty alcohols (B) and sterols (C) as main components. Fraction A inhibited the biosynthesis of cyclooxygenase (CO) and 5-lipoxygenase (5-LO) metabolites in the same intensity as the native extract SG 291, while the fractions B, C and beta-sitosterol showed no inhibitory effect on both enzymes of the arachidonic acid pathways. Therefore, the CO and 5-LO inhibiting principle of Sabal serrulata extract SG 291 must be localized in the acidic lipophilic fraction (SLF). The CO and 5-LO inhibitory effects may give an explanation for the in vivo observed antiphlogistic and antiedematous activity of the lipophilic Sabal serrulata extract SG 291.