The ability of the promotor/enhancer region of the mouse ornithine decarboxylase gene to respond to various stimuli was studied. This region was subcloned into multiple fragments and these were inserted in front of the chloramphenicol acetyltransferase gene on an expression vector, pBLCAT3. These ODC/CAT constructs were transfected into a mouse macrophage-like cell line, RAW264. The transfected cells were stimulated by bacterial lipopolysaccharide, 8-bromo cAMP or both followed by analysis of chloramphenicol acetyltransferase activity. Optimal inducible chloramphenicol acetyltransferase expression was obtained when sequences from -90 to +12 (with respect to the transcriptional start site) were tested in cells treated with a combination of lipopolysaccharide and 8-bromo cAMP. A putative cyclic AMP response element located at -48 was altered by site-directed mutagenesis but these alterations did not diminish activity in response to stimulation with lipopolysaccharide and 8-bromo cAMP.