Flavone acetic acid (FAA) is a semi-synthetic flavonoid characterised by potent immune-modulatory and antivascular activity on mice but not in humans. Previously, the synthesis and cytotoxic activity on a human adenocarcinoma cell line of coumarin-, flavanon- and flavonol-derivatives of FAA were described. These analogues were able to induce the reduction of lysosomal neutral red uptake at 5 x 10(-5) M concentration and some of them were more effective than FAA. Some of these derivatives were selected to investigate their ability to exert immune-modulation on a human model, by using the most potent analogue that has emerged thus far, 5,6-dimethylxanthenone-4-acetic acid (DMXAA), as a reference compound. We investigated the cytotoxicity of the selected derivatives on two human ovarian adenocarcinoma cell lines and their ability to activate the immune system by inducing lytic properties, TNF-alpha and nitric oxide in human monocytes. The immune-modulating activity was assessed by treating a cell line of human monocytes (Mono Mac 6, MM6) with FAA-derivatives alone or in association with lipopolysaccharide (LPS). None of the tested molecules showed any significant ability to directly affect tumor cell proliferation, whereas they were able to induce the lytic properties of MM6 cells. In particular, two coumarin derivatives, a and d, and the flavonol acetic acid, l, showed comparable results to DMXAA. The combination with LPS did not lead to synergistic interactions in the induction of the lytic properties of MM6, but it significantly increased the release of TNF-alpha, especially after 4 h of treatment. Instead, the maximum release of nitric oxide (NO) was detected after 24 h of treatment and after exposure to the FAA derivatives alone. Derivative a combined with LPS and analogue d alone were able to induce a higher TNF-alpha and NO release, respectively, whereas flavonol acetic acid was characterised by a strictly similar activity to DMXAA.