On 28 July 1977 an unusually cloud-ftee nighttime thermal infrared image of the midwestern and northeastern United States from the NOAA 5 satellite enabled detection of more than 50 urban beat islands. Analysis of digital data from the satellite for selected cities yielded maximum urban-rural temperature differences ranging from 2.6 to 6.5°C. Through computer enhancement and enlargement of the satellite imagery, the urban beat islands of St. Louis, Washington, DC and Baltimore can be depicted at a usable scale as large as 1:500 000. A comparison of the enhanced thermal infrared imagery with the 1970 U.S. Census maps of urbanized areas for the three cities indicates the extent of possible urbanization changes in the last seven years.