Two different types of low-cost, wide-band, infrared radiometers together with a high performance, internally calibrated radiometer -designed specifically for the validation of high quality satellite radiometers (SISTeR) are evaluated for use in validating ATSR sea surface temperature (SST) measurements. The instruments were evaluated as part of the Mutsu Bay Experiment in Japan during July/August 1996 and in subsequent laboratory work. Careful consideration of various physical and environmental factors is necessary for accurate validations. These factors include: reflected sky radiation, sun-glint; and solar heating of the instruments, These are discussed in this paper along with the need for regular and frequent calibration of the instruments. Preliminary analysis of results suggests that low-cost radiometers can be effectively, in a limited range of conditions, for validation of satellite SST's.