Pharmaceutical preparations derived from natural sources such as vegetables often contain compounds that contribute to the antioxidant defence system and apparently play a role in the protection against degenerative diseases. In the present study, commercial preparations containing extracts of turmeric, artichoke, devil's claw and garlic or salmon oil were investigated. The products were divided into fractions of different polarity, and their antioxidant activity was determined using the Trolox equivalent antioxidant capacity (TEAC) assay. This test is based on the efficacy of the test material to scavenge 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) derived radicals. Total phenols were determined in all fractions as well as specific carotenoids in the most lipophilic fraction to assess their contribution to the antioxidant activity. For comparison, the radical scavenging effect of selected constituents of the extracts such as curcumin, luteolin, kaempferol, chlorogenic acid, harpagoside, beta-carotene and alpha-tocopherol was investigated and compared with that of Trolox. Curcumin, luteolin, kaempferol, chlorogenic acid and beta-carotene showed an antioxidant activity superior to Trolox in the TEAC assay; harpagoside was barely active. All fractions of the turmeric extract preparation exhibited pronounced antioxidant activity, which was assigned to the presence of curcumin and other polyphenols. The antioxidant activity corresponding to the artichoke leaf extract was higher in the aqueous fractions than in the lipophilic fractions. Similarly, devil's claw extract was particularly rich in water-soluble antioxidants. Harpagoside, a major compound in devil's claw, did not contribute significantly to its antioxidant activity. The antioxidant capacity of the garlic preparation was poor in the TEAC assay. That of salmon oil was mainly attributed to vitamin E, which is added to the product for stabilization. In all test preparations, the antioxidant activity was significantly correlated with the content of total phenolic compounds.