The effect of the crude extract and of two alkaloid fractions prepared from Mahonia aquifolium on interleukin-8 (IL-8) production in the lipopolysaccharide (LPS)-stimulated human monocytic cell line THP-1 was studied. The production of IL-8 by cells stimulated with 20 ng/ml LPS after 48 h treatment with 20 microg/ml crude extract was inhibited by about 30 %. LPS-stimulated cells treated with 0.1 microg/ml bisbenzylisoquinoline alkaloid fraction exhibited a 40% inhibition of IL-8 production in comparison with control cells. The fraction of protoberberine alkaloids had no significant inhibitory activity. Weak or no inhibition of IL-8 production was found after treatment with 0.5 microg/ml of protoberberine alkaloids berberine and jatrorrhizine and with berbamine from the group of BBI alkaloids. In contrast, the production was inhibited after treatment with BBI alkaloids baluchistine (about 20%) and aromoline (up to 30%).