An experiment tested the hypothesis that the masking effects of two nonoverlapping forward maskers are summed linearly over time. First, the levels of individual noise maskers required to mask a brief 4-kHz signal presented at 10-, 20-, 30-, or 40-dB sensation level SL were found. The hypothesis predicts that a combination of the first masker presented at the level required to mask the 10-dB SL signal and the second masker presented at the level required to mask the 20-dB SL signal, should produce the same amount of masking as the converse situation i.e., the first masker presented at the level required to mask the 20-dB SL signal and the second masker presented at the level required to mask the 10-dB SL signal, and similarly for the 30- and 40-dB SL signals. The results were consistent with the predictions.