Abstract.Changes in the bioelectric field potential at the apical end of dark‐grown soybean (Glycine max)hypocotyls after exposure to several wavelengths of light have been monitored with an electrometer. A small dose of 660 nm radiation brings about a rapid positive rise in the potential. A following small dose at 760 nm prevents the increase, suggesting a phytochrome action. Pre‐irradiation with 660 nm enables a subsequent larger dose of 760 nm, which by itself is without effect, to elicit a delayed rise in the potential.A large dose at 710 nm induces a delayed increase in the field potential. The increase is prevented by a following dose at 550 nm, but not at 660