The appearance and development of prochymosin- and pepsinogen-producing cells were investigated in the ovine abomasum from fetus to adult using immunohistochemistry. Prochymosin immunoreactivity appeared first in the proper gastric glands of the 100-day-old fetus. The intensity and distribution of prochymosin-immunoreactive cells increased gradually with the progress of gestation, and their most intense immunoreactivities and widest distribution were observed in 3-day-old lambs. They were subsequently reduced throughout postnatal growth. A few prochymosin-immunoreactive cells were scattered in the glands of adult sheep. Pepsinogen immunoreactivity appeared at first in a small number of cells in the base of some proper gastric glands of 120-day-old fetuses. After 130 days, pepsinogen-immunoreactive cells increased their staining intensities and distribution. They reached a peak in area at 21 days, which is comparable to adult sheep. In the pyloric glands, prochymosin- and pepsinogen-immunoreactive cells appeared from 100 and 130 days, respectively. Numbers were reduced in comparison to gastric glands and their occurrence was capricious. The results demonstrated that the ontogeny of prochymosin- and pepsinogen-immunoreactive cells in the abomasum of sheep is more similar to that in cattle than to that in the goat. The present data will contribute to the overall understanding of the development of ruminant gastric proteases.