Phenolic (vanillic, p-coumaric, ferulic and p-hydroxybenzoic) acids inhibited corn seedling radicle elongation in bioassay studies, especially at solution concentrations exceeding 1.0 × 10−4M. Radicle growth inhibition among hybrids was different when p-coumaric or ferulic acids were assayed, suggesting that corn sensitivity to phenolic acid phytotoxicity may be hybrid dependent. Key words: Allelopathy, phenolic acids, radicle growth inhibition, corn, Zea mays L., hybrid response