The study describes the ability of electric and magnetic fields to substitute for nerve growth factor in the stimulation of neurite outgrowth in a subline of PC-12 cells, derived from a pheochromocytoma in rat adrenal medulla. The cells were plated on collagen-coated, 60-mm plastic petri dishes and exposed to sinusoidal 50-Hz magnetic fields for 22 hours in a 5% CO2 incubator at 37 C. Two 1000-turn coils, 20 cm in diameter, were assembled in a Helmholtz configuration to generate a magnetic field in a vertical orientation, thereby inducing a companion electric field. A co-netic metal shield housed the control samples in the same incubator. Total cells and number of cells with neurites at least as long as the cell diameter or having a growth cone were counted within an annulus of 1.7 to 1.8 cm radii. Sham exposure demonstrated no difference in % of cells with neurites between the exposed and control locations in the incubator. Exposures were done at 420, 230, 120, 42, 31, 22, 9 and 4.2 milliGauss (mG). At the dish radius of 1.7-1.8 cm these flux densities induced electric fields of 115, 63, 33, 12, 8.5, 6.0, 2.5 and 1.2 microV/m, respectively. At each field strength, there were two control dishes and six exposed dishes, except for 5 exposure dishes at 120 mG. The results demonstrate that electric and magnetic fields stimulate neurite outgrowth in a field strength-dependent manner between 22 and 42 mG (6.0 and 12 microV/m), reaching an apparent stimulation plateau between 42 and 420 mG(12 and 115 microV/m).