Recent studies have promoted using soil phosphate analysis to detect ancient Maya sites by delimiting areas of occupation based on decomposed organic matter. Refuse associated with human activity increases organic matter around areas of ancient human habitation. Theoretically, the highest concentration of organic matter—detectable by phosphate analysis—should be directly associated with areas of refuse disposal. Thus, the objective of this study is to investigate the potential of phosphate analysis to detect residential middens in Piedras Negras, Guatemala. This paper presents the results of a sensitive, in-field phosphate analysis method applied as a midden prospection tool in residential areas. Phosphate concentration is correlated with artifact data obtained from a total of 37 test pits excavated in areas of varying phosphate concentration in three residential sites. A positive correlation between phosphate concentration and ceramic density indicates the potential of this method in defining and orienting excavations of residential areas. © 2001 John Wiley & Sons, Inc.