The fate of 3,4-dichloroaniline (DCA), a major metabolite of the herbicide propanil (3′,4′-dichloropropionanilide), in rice (Oryza sativa L.), soil, water, and aquatic organisms was determined in rice-paddy microecosystems. Soil, treated with 10 ppm DCA, was placed in glass chambers, planted to rice, then flooded when the rice reached the two-leaf stage. After flooding, four species of aquatic organisms were added. The concentration of DCA and metabolites in soil, rice, water, and aquatic organisms was determined over a period of time. A maximum of 2.8% of the total radioactivity applied to soil desorbed or leached into water. DCA recovered from water decreased from 12 to 1% of the total radioactivity in water between 1 and 30 days after flooding. Between 10.5 and 18.5% of the radioactivity remaining in soil at the end of the experiments was extractable. Of the radioactivity recovered, between 5 and 11% was DCA, and up to 6 to 19% was 3,3′,4,4′-tetrachloroazobenzene (TCAB), these percentages being dependent on exposure time. Rice accumulated 0.5% or less of the total radioactivity in soil. Only 35 to 55% of the accumulated radioactivity was extractable. Very small amounts of radioactivity were accumulated by aquatic organisms.