The effects of gallic acid on the gene expressions of inducible nitric oxide synthase (iNOS) and the cytokines interleukin (IL)-1, IL-10, IL-12, IL-18, TNF-alpha, and interferon (IFN)-gamma were investigated by reverse-transcription polymerase chain reaction (RT-PCR). The experiments were performed in parallel in non-infected and in L. major-infected RAW 264.7 cells and the expression profiles were compared with those mediated by IFN-gamma plus lipopolysaccharide (LPS). The infection per se induced the expression first of IL-1 and TNF-alpha mRNA, later that of IL-10 mRNA. Gallic acid induced low and transient levels of TNF-alpha and IL-10 in non-infected cells, and it clearly enhanced and prolonged iNOS and cytokine mRNA expressions in Leishmania-parasitised cells. Interestingly, and in contrast to activation by IFN-gamma/LPS, gallic acid also stimulated Leishmania-infected cells to produce IFN-gamma mRNA. For IFN-alpha, a sandwich immunoassay was performed to determine its amount present in the supernatant of gallic acid-stimulated RAW 264.7 cells. In showing predominant stimulation of infected cells and the induction especially of IFN-gamma, a cytokine that plays a central role in antimicrobial macrophage and T cell regulation, these data provide the basis for an immunological concept of gallic acid and possibly other plant polyphenols for their beneficial effects in various infectious conditions.