The satellite cell is responsible for growth and repair of postnatal skeletal muscle. We investigated the expression of the myogenic regulatory gene (MRG) family in these cells in the stages from quiescence to fusion. Using polymerase chain reaction amplification of reverse-transcribed RNA (RT-PCR) isolated from adult rat satellite cells, we demonstrated a temporal sequence of gene activation, which is distinct from that previously observed in embryonic somatic cells. No MRG expression was detected in predominantly quiescent cells. MyoD is activated by 12 h in cell culture, prior to the first evidence of proliferation. MRF4 and myf-5 appear by 48 h and may be associated with the first division cycle. Myogenin is not detectable until 72 h after satellite cell recovery from the muscle fiber, coincidental with the first evidence of differentiation.