The photometer measurement of respirable aerosol mass concentration is widely employed in air pollution monitoring. Using the Mie theory of light scattering and the built-in optical parameters of some photometers, the output signal was theoretically calculated and related to the real aerosol mass concentration. The definition of the mass sensitivity in combination with the device calibration constants enables the photometer response bias calculation as a function of the main aerosol parameters (index of refraction, particle density, particle size distribution). The respirable fraction＇(Soderholm (1989) Ann. occup. Hyg. 33, 301-320; Cornite Europeen de Normalisation (1993) EN 481; International Standards Organisation (1993) DIS 7708; American Conference of Governmental Industrial Hygienists (1994) Cincinnati, OH, pp. 42-45) of the ambient aerosol was used as a reference concentration for the calculation of the bias. The photometer response bias maps were built for four mineral dusts and a wide range of their aerosol distributions. The method makes possible an estimation of the photometer response bias in measuring various aerosols when the instrument is calibrated against any other aerosol.