Developmental effects were studied in pregnant albino-mice after exposures to a static homogeneous magnetic field (1 T) on days 7, 10 or 13 post conception (p.c.). These days correspond approximately to the 16th, 28th or 42nd day p.c. in human development and represent stages of increased sensitivity. Intrauterine effects (after exposures on days 7 or 10 p.c.) were evaluated. They included lethality, external malformations, disorders in the fetal skeleton and fetal weights. The evaluation of postnatal effects (after exposure on day 13 p.c.) included body-weight, brain weight, diameter of neocortex and commissures and the alignment of cortical neurons up to day 46 p.c. According to all these criteria, no development effects were observed after exposure to the magnetic field. Transient effects, that can be compensated or have no biological relevance cannot be excluded.