Combination bandsgenerated by a pure tone and a narrow band of noise are detected and produce masking patterns in the frequency region below the primaries (Greenwood, 1969a, 1969b, 1970, 1971a, 1971b). Virtually identical masking patterns are produced by noise bands of external origin, situated on the low‐frequency side of a more intense tone. Patterns in both cases take the form of elevations that merge with, or stand in isolation from, thelow‐frequency side of the masked audiogram produced by the tone, depending on the separation of the band from the tone. This study of masking by bands of external origin was undertaken (a) to measure the effect, if any, of the higher‐frequency more intense tone on masking exerted by the noise of known intensity; (b) to permit, thusly, inferences to be made as to the effects of a lower primary on the masking exerted by acombination bandbelow it; (c) to obtain signal/masker ratios for use in estimating combination band levels; and (d) to study one experimental situation bearing on the “additivity of masking” problem. Conclusions pertaining to these objectives are, respectively: (a) that the presentation of a higher‐frequency more intense tone with a band of noise does not increase the masking maximum produced by the noise; (b) that it is plausible to assume that masking by combination bands is not affected by the lower primary above it; (c) that the obtained signal/masker ratios can be used to estimate combination band levels; and (d) that, although the tone does not increase masking by the noise, weaker lower‐frequency noise can affect masking by the tone.