The use of Landsat thermal infrared imagery gives a direct way of quantitatively monitoring the evolution of low-amplitude thermal anomalies. Using nighttime Landsat thematic mapper images of Vulcano and Stromboli volcanoes on October 23, 1986, we have developed a simplified method for correcting atmospheric effects. We were then able to identify thermal anomalies around the craters. Part of the Stromboli lava flow, formed 1 year earlier, was also still warm enough to be detected. We obtained fairly accurate estimates of relative surface anomaly radiative heat fluxes: 29¿5 W m-2, 21¿4 W m-2, and 37¿5 W m-2 for the Stromboli craters, Stromboli lava flow, and Vulcano crater, respectively. Accounting for the convective heat loss significantly increases the estimates of the relative internal heat flux of geothermal origin; we found values of 370¿60 W m-2 for the Stromboli crater region, 220¿50 W m-2 for the Stromboli lava flow, and 270¿60 W m-2 for the Vulcano crater. Despite the low precision, these values are much higher than the 53--62 W m-2 limit (defined by Cassinis and Lechi, 1974) as the threshold where the geothermal flux can affect ground temperatures. Our study provides a unique systematic definition of thermal volcanic features found on Stromboli and Vulcano, the spatial extents of the anomalies, and their fluxes and associated errors. ¿ American Geophysical Union 1994