Glasshouse experiments were conducted to determine the phytotoxic effect of triallate [S-(2,3,3-trichloroallyl)-diisopropylthiocarbamate] granules on oat (Avena sativa L. ‘Kelsey’). The sphere-of-influence of the granules was found to diminish rapidly with increase in the horizontal distance from the tips of the caryopses. At a distance of 10 mm from the caryopsis tip there was no significant effect on the growth of the oat seedling. The need for the granules to be in close proximity to the developing coleoptile could not be counteracted by increasing the number of granules per caryopsis once the granules were 10 mm or more from the caryopsis. These results give cause to seriously question the generally held belief that triallate disperses through the soil in a volatile phase. Extension of the first leaf and mesocotyl was inhibited much more readily by triallate than coleoptile extension, which was stimulated by a number of treatments. When granules were left on the soil surface of sub-irrigated pots the phytotoxic effect seemed to be mediated through triallate-exposure of the coleoptile tip.