Objective measurements or rates of deforestation, especially in the tropics, have been elusive. We report the development and use or a series of techniques for use of existing satellite imagery for measurement or rates of deforestation in the tropics. The techniques have been applied in the Brazilian state of Rondonia in the southwestern Amazon Basin, the site of a large Brazilian resettlement project, started in the early 1970s. Application of special techniques for detecting change using Landsat imagery showed that between 1976--1978 and 1978--1981 the rate of deforestation increased by a factor of 2 from 620 km2 yr-1 to 1270 km2 yr-1 in the 109,000-km2 section of Rondonia studied with Landsat imagery. A combination of the Landsat and NOAA 7 advanced very high resolution radiometer imagery was used to provide an estimate of the total extent of deforestation in Rondonia by 1982. The area was 11,400 km2 or 43% of the total area of the project and 6% of the state. The techniques are highly promising and, with further development, can be used to estimate the extent and rates of deforestation globally. ¿American Geophysical Union 1987