The present study investigated the effect of the number of spectral components on the threshold in quiet of infrasound stimuli. Stimuli with one, two, or three sinusoidal components were presented monaurally to the ear with a low-distortion infrasound reproduction system. All components of the complex tones had the same level relative to their respective pure-tone threshold. The data are consistent with the assumption of a (perceptually weighted) intensity integration at threshold: The level at threshold for each component is 3 dB lower when two components were presented simultaneously. Thresholds decrease further, when a three-tone complex is used.