The ontogeny of ovine muscle was studied. 23 single fetuses aged between 48 and 125 days of gestation (dg) were collected from abattoirs. The weight and crown-rump length of fetuses were measured and gestational age was estimated. Semitendinosus muscle (ST) or hind limbs (for smallest fetuses) were dissected and stained for alkali-stable ATPase and slow myosin heavy chain (MHC) antibody and also examined under the electron microscope (EM). Based on histochemical, immunohistochemical and electron microscopy study, qualitative findings were obtained. The results suggested that some secondary fibres early express slow MHC. These small, slow expressing secondary fibres adjacent to the large, slow expressing primary fibres began to occur at 52 dg and these increased in size at around day 69 and then migrated around 87 dg to act as a scaffold for the next generation of secondary (tertiary) fibres. We conclude that some of the large, central, slow expressing (also less intensely stained with alkali-ATPase) fibres at near term sheep fetus might be secondary fibres.