Abstract: Harmonic generation in the nearfield of the harmonically excited circular piston source is considered. The quasilinear parabolic model is used to determine the averaged pressure over the planar receiving transducer of a diameter equal to that of the source. The model is then simplified by assumption that the receiving transducer covers the entire section of the acoustic beam. The derived general expressions are used in sample computations of the second and third harmonic components of the averaged pressure in distilled water. The results of computations are compared with the results obtained from direct numerical integration (so called Bergen code) of the KZK equation and with the experiment conducted in distilled water.