The mesencephalic neural plate of early-somite-stage mouse embryos differentiated underneath the renal capsule to form mostly neural tissues together with other tissues some of which were probably of neural crest cell origin. The capacity to form non-neural tissues such as skeletal tissues and melanocytes was lost at about the 5-somite stage. The lateral areas of the plate tended to form non-neural tissues more than the medial areas. The cephalic neural plate of presomite head-fold-stage embryos differentiated extensively to form both ectodermal and mesodermal tissues. However, upon completion of neurulation, the mesencephalic neuroepithelium of forelimb-bud-stage embryos gave rise to neural tissues only. Therefore there is a progressive restriction in the histogenetic capacity of the mesencephalic neural plate during neurulation and this could be attributed to the cellular commitment for neural differentiation and the loss of the neural crest cells.