Intensive agriculture associated with the use of large amounts of different pesticides, together with the growing concern about the potential contamination of ground water, have brought about the need for developing fast screening methods. This work presents the automation of an enzyme-linked immunosorbent assay for atrazine by means of a flow-through system. Three different solid supports for antibody immobilization were compared in a direct competitive assay format. Sensitivity reached in all cases was below the maximum level allowed in the EU (100 ng L-1). Cross-reactivity of atrazine-related compounds was also studied. The performance of the different supports is discussed regarding sensitivity and immunosurface regeneration.