This paper presents a rational, explicit and practicable approach for incorporating the spectral nonuniformity within a narrow band into a nongray analysis of radiative heat transfer. First of all, emphasis is placed on describing the necessity of a new approach for treating this kind of spectral nonuniformity. In the development of this new approach. attention is paid to securing rationality and explicitness even when the approach is applied to nonisothermal fields. This aim is achieved based on the fact that the line center of each absorption line does not move even if the gas temperature varies. Validity of the proposed approach is demonstrated in a typical nonisothermal field. Furthermore, the extension of the proposed approach to the mixture of more than one infrared-active species is discussed and its validity is examined.