Bies and Hansen [J. Acoust. Soc. Am.88, 2743–2754 (1990)] have proposed an alternative formulation of the relationship between noise exposure and noise‐induced hearing impairment to that presented in International Standard ISO 1999, in which they assume that presbycusis and noise‐induced permanent threshold shift (NIPTS) are additive on an antilogarithm basis. Data concerning deterioration in hearing threshold levels at 4000 Hz due to aging in war veterans with NIPTS do not support the Bies and Hansen assumption but provide support for the formula for combining presbycusis and NIPTS incorporated in International Standard ISO 1999.