The effect of exposing tame oat (Avena sativa L. ‘Hudson’) to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate] during seed imbibition was investigated in a growth cabinet at 21 C in the absence of light. Caryopses were imbibed in 0.0, 1.5, and 3.0 ppmv aqueous dilutions of trifluralin and triallate for up to 10 h, after which germination was continued in distilled water. Germination was not affected following imbibition in either herbicide. Both herbicides produced distinct visual symptoms of herbicide injury during subsequent seedling growth. Coleoptile length of 5-day-old seedlings was reduced following imbibition in a 1.5-ppmv dilution of either herbicide. Triallate at 1.5 ppmv resulted in a reduction in shoot dry weight. Both herbicides were largely excluded from embryos of imbibing caryopses. Seedlings were unaffected when cultured from embryos excised from caryopses imbibed in trifluralin and triallate dilutions. Seedling phytotoxic effects resulted from residual activity of trifluralin and triallate retained by the pericarp and testa of imbibed caryopses. Presence of the hull during imbibition decreased the phytotoxic effect of both herbicides on shoot growth. These findings suggest that germinating seedlings of Avena spp. may be affected by trifluralin and triallate at an earlier stage than previously realized.