The effect of metham on cotton stand establishment, growth, mycorrhizae development, and yield was studied in a 2x3 factorial experiment conducted in three fields in the San Joaquin Valley of California. Main-effect comparisons included nontreated seed vs. seed treated with Apron plus Nu-Flow ND and metham applied to the soil at 0, 50, or 100 gal/A. In one location, stand was improved with metham but yield was reduced due to reduced root infection by mycorrhizal fungi. In another location, metham had no effect on mycorrhizae and both stand and yields were increased compared to the nontreated soil. In the third location, metham negatively affected mycorrhizae and plant development but had no effect on stand or yield.