Work in bioelectromagnetics has long been plagued by problems with replication. This includes experiments done on electromagnetic (EM) field-induced effects in chick embryos. Our laboratory investigated responses of embryos from two flocks of White Leghorn hens. Both flocks were studied simultaneously, and it was found that they responded differently to EM field exposures. Embryos were exposed to 60 Hz, 8 microT EM fields prior to placement in an anoxic chamber. Following re-oxygenation, survival in controls was 34.6%, exposed flock 1 survival was 62% (P < 0.0001) and exposed flock 2 survival was 43% (P < 0.0136). P values are from comparison of data between EM field exposed embryos (flocks 1 and 2) versus controls. In order to induce maximum protection in flock 2, (approximately 62% survival), embryos required a longer exposure time at higher magnetic field strengths. These results reinforce the concepts that genetics are important in determining whether or not chick embryos will respond to EM field stimulation. A broader look at the role of genetic factors emphasizes that these variations in response to external stimuli (e.g., drugs, radiation, and EM fields) are found in all areas of biological research (cell culture, chick, rat, and human studies). The present study suggests that genetics may be a prime cause of the difficulties encountered in replication studies in the field of bioelectromagnetics. We conclude that replication studies should not be undertaken unless care is taken to insure that exactly the same strains of cells or animals are used. Researchers should also first confirm that the responses of their model to non-EM field stimuli are similar to that obtained in the original study.