The radial motion of a gas bubble has been widely investigated in various studies using different theoretical models. The aim of this study is to compare, qualitatively and quantitatively, the results obtained by optical recording with those of a theoretical model. Bubble oscillations were optically recorded using an ultrafast digital camera, Brandaris. The radius-time, R(t), curves are directly computed from 128 video frames. The resting diameters of the air bubbles were 26-100 /spl mu/m. The ultrasound field was defined as an 8 cycle pulse at a frequency of 130 kHz generating an acoustic pressure of 10-150 kPa. The time and the frequency response of the bubble radial motion were compared to the Keller model. From the results, it is concluded that the Keller model can be used to accurately predict the fundamental and harmonic behavior of gas bubbles.