A new method for the estimation of the voice open quotient is presented. Assuming abrupt glottal closures, the glottal flow waveform is considered as the impulse response of an anticausal two-poles filter. It is defined by four parameters: T0, Av, Oq and αm. The last three ones are estimated by a second-order linear prediction of the inverse filtered speech. Results on synthetic and natural speech signals are reported and compared with measurements on the corresponding electroglottographic signals.