The degree of resistance to a pulsed electric current of wood in progressive stages of discoloration and decay in living trees was correlated primarily with the moisture and mineral contents of the wood. Below the fiber saturation point, the degree of resistance was correlated primarily with the amount of moisture while above the fiber saturation point resistance was correlated primarily with the concentration of mobile potassium and calcium ions. The apparatus used to produce the current and to measure the resistance to it was accurate in detecting and in indicating the stage of deterioration of discolored and decayed wood. The apparatus was tested and found to be reliable electrically within the range of resistances encountered in the trees studied.