Banana production is very important for the Ecuadorian national income, but it is also a potential source of river pollution in the country. Current research is focusing on the use of GIS to perform pesticide assessment of a river basin that includes banana as its main agricultural activity. The Agricultural Non Point Source Model (AGNPS) is being used to perform pesticide assessment in the basin. The model structure and type of needed data was identified. By applying GIS methodology, a complete set of cartographical information was obtained to supply input data to the pesticide model. In addition, ready-to-print maps were useful by-products for farmers.