This paper reports on a rapid ethnographic assessment methodology (REA) that was developed as an essential component of the dietary management of diarrhea (DMD) program. The DMD program is an interdisciplinary research project that has been developed to design intervention programs to reduce or eliminate the nutritional complications of diarrhea in Peru and Nigeria. Anthropological data gathering was an important component of the intervention design, but time and budgetary constraints required a rapid methodological approach. This paper outlines the REA methodology, describes the advantages and disadvantages of the approach, and discusses future applications for international primary health care interventions.