Résumé : The alpha-foetoprotein (AFP) gene is extinguished in hybrids formed between hepatoma cells (expressing cells) and fibroblasts (non-expressing cells). Transfection experiments with constructions containing segments from the promoter region of the AFP-gene, placed upstream of an ubiquitously expressed promoter (the Herpes virus thymidine kinase gene promoter), showed that the AFP gene-derived sequence contains at least one negative element active in fibroblasts (while this sequence behaves as an enhancer in hepatoma cells). We identified such a fibroblast negative region, localized between nucleotide positions -80 to -38 (FNE1). Gel retardation experiments showed that FNE1 specifically binds fibroblast nuclear proteins, generating three complexes. The sequence from -57 to -43 was shown to be responsible for both the formation of these complexes and the negative activity of FNE1. These results suggest that the binding of nuclear factors to the AFP promoter region contributes to silencing the AFP gene in non-expressing cells, such as fibroblasts, and thus to establishing lineage-specific expression of the AFP gene.