The results of a preliminary study on the effects of a magnetic field on some morphogenetic processes in Rana esculenta and Bufo vulgaris embryos are reported. The point of a magnetic needle was brought to a distance of 0,5 mm from the optic vesicle field of embryos at early neurula stage (neural folds open), and a magnetic field was applied for 10' to 40'. In a large percentage of embryos the eye development was completely lacking, or it was greatly reduced. However the growth rate and the general morphology were the same as in control embryos. The histological sections of a Rana esculenta embryo showed, instead of the normal eye, a small aggregate of cells, supplied by a very thin optic nerve; the oculomotor muscles were remarkably reduced. The chiasma opticum appeared to be asymmetrical, and there was no fiber of tractus opticus in the counterlateral part of diencephalon. On the contrary, in Bufo embryos optic fibers were present in both walls of the diencephalon; the asymmetry of the optic tectum was negligible. Some characteristic features of the partially athrophic eye in Bufo are also described.