Induction of c‐fos expression occurs following treatment of diverse cell types with agents that trigger mitogenesis, differentiation or membrane depolarization. We suggest that c‐fos may be regarded as a marker for a set of rapidly induced genes (termed cellular immediate‐early genes) whose function is to couple extracellular stimulation to long‐term responses. In the brain, these genes may contribute to the adaptive alterations involved in neuronal plasticity.