AbstractStudies have been made of the d.c. semiconductive behavior of fibers and solid gels of DNA. The semiconductive behavior under high vacuum is similar in solid gels of DNA and stretched fibers of DNA measured along and across the fiber axis. Photoelectric effects have been studied, and an action spectrum is reported which agrees with the absorption spectrum of DNA. No photoelectric effects are observed at wavelengths corresponding to the thermal energy gap. The temperature dependence of the photocurrent has been determined, and the effects of air, oxygen, and nitrogen at different pressures on the photocurrent have been measured.