A process for removing selenium and nitrate from agricultural drainage water using algae and anaerobic bacteria was studied in a field system. Algae were grown in high-rate ponds containing drainage water, and the 178-± 99-mg/L culture took up 18 ± 13 mg/L NO3- – N. The algae and drainage water were then transferred to anoxic units where denitrifying and selenate-reducing bacteria, feeding on algae, reduced NO3–N from 100 ± 24 mg/L to less than 10 mg/L at times. Soluble selenium concentration, which was 200–400 mg/L in the influent, decreased only slightly in anoxic units, but speciation of effluent selenium showed that selenate was completely reduced to selenite and other reduced forms. Addition of 10–20 mg/L ferric chloride to the effluent reduced soluble selenium to 7–12 mg/L. Selenium reduction was not inhibited by 2000–4000 mg/L sulfate. Algae not used by denitrifying and selenate-reducing bacteria were fermented to methane in unmixed cylindrical digesters where methane production averaged 0.16 L/g volatile solids introduced.