The outgoing longwave radiation (OLR) fluxes derived from NOAA-SR (1974–78) are found to he consistently higher than those from NOAA-7 (1982 onward) over a large part of the tropical belt. Analysis of the variation of the mean July–August OLR and the rainfall over the Indian region suggests that the lower values of OLR in the latter period cannot be attributed to more intense convection. Thus, the consistently lower values of OLR in the latter period over a large part of the tropical belt (including the oceanic regions) may be a manifestation of a systematic bias arising from various factors such as changes in instruments, equatorial crossing time, etc. Obviously, if such a bias is present, it has to be removed before the dataset can be used for the study of interannual variations. If the bias is removed by a simple method based on the variation of convection over the entire tropical belt, the OLR variations over the Indian region become consistent with the rainfall variations.