Recent validation studies have confirmed that the first along-track scanning radiometer (ATSR) can retrieve sea surface temperature (SST) to an accuracy of 0.3K even in the presence of heavy atmospheric aerosol. However, using the standard (pre-launch) retrieval, this accuracy is achieved only when data from all three thermal channels (3.7, 11 and 12 μm) are available; in the absence of 3.7 μm data, retrieved SSTs are subject to significant cold bias. As 3.7 μm data are useful only for nighttime observations, and ATSR's 3.7 μm channel failed in May 1992, only 11 and 12 μm data informed SST derivation for most of the 1991 - 1996 mission. We demonstrate the potential for improvement in this retrieval, based on comparison of observed brigthness temperatures with precise SSTs derived using 3.7 μm data. A reduction in global-mean cold bias from >0.6K to