The entry of microorganisms into the body induces inflammatory processes. During this process a sequence of cellular, humoral, non-specific and specific actions are evoked to combat the infection. Macrophages and granulocytes, which are developed from a common progenitor cell, are the cellular components of the specific and non-specific immunoreaction. MRP14 (Macrophage migration inhibitory related protein) and MRP8, two S-100 proteins contained in high concentrations in these cells are obviously essential for adhesion and migration of monocytes and granulocytes. To investigate the transcriptional regulation of these genes we cotransfected constructs expressing CAT under control of the MRP14 promoter and expression constructs of C/EBP alpha and v-myb, two transcription factors involved in myeloid/monocytic differentiation. Transfection with C/EBP alpha revealed a massive enhancement of the MRP14 promoter in both, HL 60 cells (granulocytic differentiated) and L132 fibroblasts. In contrast, v-myb reduces MRP14 promoter activity. Northern blot analysis of L132 cells transfected with the C/EBP alpha expression vector demonstrate that C/EBP alpha is sufficient to enhance MRP14 expression in the context of the whole genome.