Greenhouse studies were conducted to evaluate and compare herbicide safeners for protection of corn and sorghum from herbicidal injury from metolachlor, primisulfuron, and the interaction of primisulfuron with terbufos, an insecticide. With the exception of CGA-133205 which killed corn, the safeners oxabetrinil, flurazole, naphthalic anhydride, dichlormid, and R-29148 protected against significant injury from the interaction between primisulfuron (40 g ai ha−1) and terbufos (9.8 kg ha−1 equivalent to 750 g per 1000 m of row) and from metolachlor (6.7 kg ai ha−1). No primisulfuron-terbufos interaction was observed in sorghum and none of the safeners protected sorghum from primisulfuron injury. PRE application of the antioxidants, piperonyl butoxide and metyrapone, increased primisulfuron injury to corn. Piperonyl butoxide by itself did not influence the growth of corn seedlings, but metyrapone caused slight injury. The increased injury from piperonyl butoxide plus primisulfuron applied at 40 g ha−1 was protected by naphthalic anhydride, flurazole, and R-29148, whereas at 80 g ha−1 protection was provided by flurazole and R-29148. None of the safeners tested protected against increased injury from metyrapone. Naphthalic anhydride was also an effective safener against increased corn injury when 3000 ppm piperonyl butoxide was applied foliarly 3 d prior to primisulfuron application. 14C-Primisulfuron absorption by corn was not influenced by piperonyl butoxide or the safener, naphthalic anhydride. However, metabolism of 14C-primisulfuron was inhibited by piperonyl butoxide. This inhibition was not totally reversed by the safener, naphthalic anhydride.