Tests were made to determine whether the development of chicken embryos was altered by exposure to time-varying magnetic fields. Unipolar square waves with periods of 100μs, 1, 10, 20, and 30ms, and 20ms bipolar square and sinusoidal waves were tested. The nominal peak strength for each experiment was 1μT. Neither the morphogenesis of the embryo nor the temporal aspects of development was altered by any tested field. Fertile eggs of several different strains of chickens were also tested to determine whether strain sensitivity to certain magnetic fields can account for the reports of positive effects of magnetic fields upon development. No significant alterations were noted in the embryos of any of the tested strains. Published reports of alterations in development following exposure to similar low level magnetic fields have not been confirmed in this laboratory.