Steps on Cu(100) and various vicinal Cu(11n) surfaces were studied with the scanning tunneling microscope and the kink concentrations are determined using a recently developed method. As expected, the kink concentration in steps on the (117) and the (1 1 11) surface is lower than for steps on the (100) surface due to the repulsive interaction between steps at small distances. On the (1 1 19) surface, however, steps have a larger kink concentration. The result is discussed in the context of the recently discovered attractive interaction between steps for intermediate step distances.