A combination of field, field enclosure, and germination chamber studies was used to evaluate the effects of methiocarb [3,5-dimethyl-4-(methylthio)phenol methylcarbamate] and thiram (tetramethylthiuram disulfide) repellent seed treatments on early corn performance. The thiram treatments used (0.08, 0.4, 0.8, 0.5, 1.25, and 2.5% active ingredient by corn seed weight) had negligible effects on germination/emergence time or on corn plant heights. The thiram treatments never reduced stand counts in comparison to controls, but apparently increased stand counts in some trials, particularly under wet conditions. The methiocarb treatments evaluated (0.5, 1.25, 2.5, and 5.0% active ingredient by corn seed weight) had only occasional effects on early corn performance. However, certain methiocarb treatments advanced or retarded germination in some trials and increased plant heights in three trials. Methiocarb treatment did not affect corn stand counts in most trials, but increased or reduced stand counts in some. The reduced stand counts appear related to wet conditions and possibly to other field effects. The techniques used have application in studies of both plant and rodent responses to seed-treatment repellents.