The current program of participant observation research has its origin in the recommendations made in 1985 by the Panel on Decennial Census Methodology, Committee on National Statistics of the National Research Council. Based on a review of previous participant observation research undertaken for the Census Bureau, the panelists recommended that in hard-to-enumerate areas the Bureau use records of household composition generated by participant observers as sources of coverage data. To locate experienced fieldworkers with current or recent field contacts in neighborhoods within the test census area, universities were contacted, including departments of anthropology, ethnic studies and Black Studies, in the Southwest and throughout the United States. The three researchers who agreed to work with the Census Bureau were James Diego Vigil, John Long and Camilo Garcia Parra. Dr. Vigil selected the suburb of Pico Rivera for this research, where he had conducted studies of adolescent gangs in the 1960's and 1970's. John Long selected an area in East Los Angeles where he had both lived and done research. Dr. Garcia selected a residential area about six blocks from Long's assignment, where he anticipated a large number of undocumented Central American immigrants and serious coverage problems. Each researcher produced a separate report which covers field work methods, a comparison of their population count with the census count and an analysis of discrepancies and recommendations for improving census enumeration in this kind of neighborhood.