The loudness related to a sound may vary according to the localization of its source. This phenomenon is described as directional loudness and has been mainly observed for high-frequency sounds and for sources located in the horizontal plane. Because of the acoustic shadow of the head, the left and right ear pressures are modified depending on the source azimuth and the global loudness resulting from a summation process may vary accordingly. But directional loudness has also been reported to occur at 400 Hz, where shadowing effects are usually rather small. It might therefore be suspected that directional loudness effects could be influenced by other parameters involved in the localization process. In a previous study, a small but significant increase of loudness with increasing interaural time difference (ITD) was shown for low-frequency pure tones (200 and 400 Hz) at a low loudness level (40 phon). The present study aimed at getting insight into the potential cause and extent of this effect by assessing the loudness of similar pure tones lateralized with headphones by applying an interaural level difference (ILD) in addition to an ITD and by measuring the effect of ITD at the hearing threshold. It showed significant effects of both ILD and ITD on loudness, and no interaction between these factors. As the effects added even when the factors were contradictory, it supports the hypothesis that the effect is caused by the ITD itself and is not related to the localization process. However, the ITD effect was not significant at the hearing threshold.