The ratio of the twin boundary free energy to grain boundary free energy, δtb/δgb, for coherent twin boundary-grain boundary intersecting systems in thin foils of nickel, TD-nickel, and Inconel 600 has been measured by transmission and diffraction electron microscopy. Final, corrected mean ratios of 0·031, 0·025 and 0·022 for δtb/δgbwere obtained for nickel. TD-nickel and Inconel 600 respectively. Using experimentally measured and estimated values of δgb, the twin boundary free energy δtb, for nickel, TD-nickel and Inconel 600 was observed to be approximately 27, 27 and 19 ergs/cm2respectively.