Inhibition of nitric oxide (NO) production by altering the expression of induced enzymes involved is potentially an important strategy for obtaining antiinflammatory agents. In the search for hits to obtain lead compounds for new drugs of this class, 14 synthetic chalcones derived from 2,4,6-trimethoxyacetophenone were evaluated in terms of their inhibitory action, in vitro, in relation to NO production in murine macrophages of the line RAW 264.7 induced by bacterial lipopolysaccharides (LPS). All the compounds were obtained by aldolic condensation between the acetophenone and corresponding aldehydes, under basic conditions. The mean IC(50) values, calculated through dose versus inhibitory effect curves, in four independent experiments, varied between 1.34 and 27.60microM, and were compared with the positive control, compound 1400W (IC(50)=3.78microM), a highly selective inhibitor of iNOS (induced nitric oxide synthase). Eight chalcones gave mean IC(50) values less than or equal to those obtained for 1400W, which suggests that these molecules may act as inhibitors of inflammatory process. The QSAR study reveals that electron-withdrawing groups in the B-ring seem to increase the inhibition of nitrite production, mainly when in position 2. A substitution in the ortho position of the A-ring seems to be necessary for the activity.