Most studies of the effect of static magnetic fields on living systems have yielded negative or inconsistent results (1); the exception is studies of species that incorporate ferromagnetic materials as geomagnetic sensory elements (2). Experiments on time-varying magnetic fields have been fewer and more difficult to interpret (3). A therapeutic technique for accelerating repair in bone nonunions that subjects the site to a time-varying magnetic field (4) has achieved a measure of acceptance in the clinical community (5). However, the mechanism underlying this procedure is still largely unexplained, in part because the narrow and repetitive pulse shape of the wave form, allegedly specific to the therapy, makes it difficult to perform and interpret in vitro cellular experiments (6).

We sought to determine the effect of sinusoidally varying mgnetic fields on DNA synthesis in cell culture, particularly the frequency and intensity response, if any. a pair of matched incubators were fitted with modified Helmholtz coils (0.5 m, inside diameter; 0.25 m long), providing a horizontal magnetic field with an active field uniformity no less than 3 parts out of 17. Either could be an experimental or control (no field) unit. Periodically the roles were switched and, at other times, both were used simultaneously as controls. An audio amplifier fed by a function generator supplied 0 to 1.0 root-mean-square ampere to either coil, enabling us to generate magnetic fields up to 1.0 X 10-.sup.3 root-mean-square tesla (T.sub.rms.) at frequencies ranging from 15 Hz to 20 kHz.

Two independent series of experiments were completed, both with human embryonic foreskin fibroblasts (7) as the test cell line.

In the first series, one frequency (76...