The paper reports on investigations on the dying effect of iron on wood. Peeled veneers of various species were immersed in FeCl3 solutions of varying concentration. The darkening of these specimens was photometrically registered. The influence of temperature upon the change of colour observed was also examined. It was found that this effect depends on the species, the concentration of the FeCl3 solution and to some extent the temperature used in the test. It was assumed that the formation of complex tannin-iron compounds accounts for this phenomenon. The probability of phenol complex compounds being involved could not be proved.