Phytoremediation is potentially effective for managing excessive selenium (Se) in drainage sediment residing in the San Luis Drain in central California. This 2-year field study examined the feasibility of amending drainage sediment (containing 4.78microgSeg(-1)) with methionine and casein to enhance volatilization without or with vegetation of Sporobolus airoides. Results show that without organic amendments, rates of Se volatilization were less than 25microgm(-2)d(-1) in all plots. After amending the sediment with 71.4mgmethioninekg(-1) soil, Se volatilization rates were 434+/-107microgm(-2)d(-1) in vegetated plots and 289+/-117microgm(-2)d(-1) in irrigated bare plots. With the amendment of 572mgcaseinkg(-1) soil, rates increased to 346+/-103microgm(-2)d(-1) in irrigated bare plots and to 114+/-55microgm(-2)d(-1) in vegetated plots. Both methionine and casein promoted biological remediation of Se via volatilization most effectively during the warmest months.