Electroglottographic (EGG) and acoustic records from 10 normal men prolonging the vowel /a/ at 60-68 dB, 70-78 dB, and 80-88 dB SPL were obtained. "Contact quotient" (EGG duty cycle) was shown to vary directly with vocal SPL. The mean contact quotient was 0.57 (SD = 0.07) and varied on the order of 1% over the course of a given phonation. "Contact index", a metric of EGG symmetry, also tended to vary with SPL. Consistent with previous qualitative descriptions of EGG morphology in modal register voice, the contact index averaged -0.52 (SD = 0.08), indicating that the EGG "closing phase" represents about 24% of the entire "contact phase". Contact index was more variable than contact quotient on consecutive EGG waves, varying by about 10% during phonation. Subjects were also instructed to produce a slow crescendo. Sound pressure and EGG data indicated that both the slope of increasing EGG contact and EGG duty cycle were significantly related to the amplitude of the acoustic signal. These results suggest that quantitative electroglottography may provide powerful insights into the control and regulation of normal phonation and into the detection and characterization of pathology.