The infrared channels of the advanced very high resolution radiometer (AVHRR) are calibrated in-flight with data acquired when the AVHRR views space and a warm target on board. This determines the two coefficients of a linear calibration equation. However, in its 11- and 12-μm channels the response of the AVHRR is nonlinear. If not accounted for, the nonlinearity could cause errors as large as 2¿C in inferred scene temperatures. Therefore NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) computes corrections to the brightness temperatures inferred from the linear calibration. This paper describes how the corrections have been calculated at NESDIS since March 1986 and presents the corrections for the AVHRRS on the NOAA 9, 10, and 11 satellites. The corrections are calculated from results of the preslaunch calibration, in which a calibrated laboratory blackbody illuminates the AVHRR. At NESDIS the calculation of the corrections differs from that of Brown et al. (1985) because NESDIS transfers the calibration of the laboratory blackbody to the internal calibration target of the AVHRR, but Brown et al. do not. The absolute a radiometric accuracy of AVHRR dat that have been corrected for the nonlinearity is approximately 0.55¿ C, of which 0.35¿C is traceable to the calibration of the laboratory blackbody. ¿ American Geophysical Union 1990