Benthiocarb S-[(4-chlorophenyl) methyl] diethylcarboamothioate which was applied postemergence, altered the growth and development of shoots of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and bearded sprangletop [Leptochloa fascicularis (Lam.) Gray] seedlings, two gramineous annual weeds commonly found in rice fields. The herbicide did not affect root development of either species. Benthiocarb retarded the growth of new leaves within the extending leaves and caused swelling of cells. The cells of the shoot apices of treated seedlings were often vacuolated. Tubular-like leaves were induced by benthiocarb, but their formation differed from that caused by phenoxy herbicides.