Aflatoxin contamination of peanut is a major threat to consumers in West Africa. High levels of aflatoxin have been reported in West and Central Africa, particularly in Niger. Field trials were conducted from 1991 to 1994 at ICRISAT Sahelian Center, Sadore Research Station near Niamey, Niger. Various production practices were compared to examine their effects on water stress and Aspergillus flavus infection and aflatoxin contamination. Different levels of water stress were achieved by varying planting date and frequency of irrigation in two resistant and two susceptible cultivars. Contamination of seed with A. flavus and aflatoxin was determined. The susceptible cultivars 28–206 and JL 24 had much higher levels of seed infection following 3 wk or more of water stress than did the resistant cultivars. Susceptible cultivars showed up to 81% seed infection. Cultivar 28–206 had low levels of contamination when there was low water stress but became very susceptible when the period of water stress increased (3 wk of drought). Seed infection by A. flavus and contamination by aflatoxin were highly correlated across years and cultivars. Although seed infection by A. flavus was very responsive to water stress in the field, aflatoxin contamination did not increase proportionally. This may have been influenced by high soil temperatures in Niger, which may exceed 40 C. Most reports indicate that a minimum of 20 to 30 d of drought is needed for significant aflatoxin contamination, but contamination was observed after 14 d of water stress in this study.