A possible influence of intense magnetic fields on the embryonic development of frogs was studied in reference to a potential hazardous problem in magnetic resonance imaging technology. Fertilized eggs of African clawed toads, Xenopus laevis, were cultured in Amphibian Ringer solution under static magnetic fields up to 6.34 T for varying lengths of time, and their cleavage and early embryonic development were followed to examine the possibility of teratogenic effects. Fertilized eggs cultured under the static magnetic field for 6 h followed normal course of cleavage and normally developed into feeding tadpoles. Results were unchanged even when fertilized eggs were cultured for 18 h from the cleavage stage to the neurula stage under a magnetic field of 4.5 T. We conclude that static magnetic fields up to 6.34 T do not affect appreciably the rapid cleavage and the following cell multiplication and differentiation in Xenopus laevis.