Over the past two decades a variety of mechanisms regulating cellular differentiation have been uncovered. These include signaling by morphogens or membrane‐associated ligands and asymmetric segregation of cytoplasmic components. Most of these processes are driven by protein coding genes. Here I describe another possible cellular differentiation mechanism that involves asymmetric segregation of micro RNAs, a group of recently discovered non‐protein coding genes that have been shown to be involved in differentiation. Bentwich, I. A postulated role for microRNA in cellular differentiation. FASEB J. 19, 875–879 (2005)