Higher harmonic frequencies of electric voltage and current are significant features of low-pressure capacitively coupled discharges. Their behaviour is quite complex since it is a function of many plasma and reactor parameters. This article deals with the influence of matching unit parameters on amplitudes of higher harmonics, which were measured by means of an uncompensated probe immersed into the plasma of an asymmetric capacitive discharge. Most of the harmonics reached their maxima in the case of optimal matching, i.e. when the RF power delivered to the discharge was maximal. However, the amount of the power delivered to the discharge did not explain the behaviour of higher harmonics sufficiently. It was shown that at our experimental conditions the behaviour of higher harmonics was determined by the sheath voltage.