The aim of the present study was to investigate whether the early modulation of the c-fos and c-myc oncogenes could give some orientation to the impact of immunomodulators on the monocyte-macrophage lineage. In order to work in a homogeneous system we used the P388D1 mouse macrophage cell-line which is considered as an almost mature macrophage. When P388D1 cells were stimulated by LPS, interferon-gamma or the association of both compounds, no direct correlation could be found between the modulation of DNA synthesis and the early expression of the c-fos and c-myc oncogenes. The positive regulation of Ia antigen expression seemed to correlate with the absence of induction of c-fos oncogene