The effects of three phenolic antioxidants, butylated hydroxyanisole, butylated hydroxytoluene and propyl gallate on the mutagenic activity of propane sultone were studied using barley as the test system. The antioxidants produced seedling injury marginally but did not produce any chromosomal aberrations. When administered either prior to propane sultone treatment or in a mixture with it, the seedling injury, chromosomal aberrations, mutations per 100 M1 spikes as well as M2 chlorophyll mutation frequency, were enhanced. On the other hand, however, posttreatments reduced M1 spike sterility, mutations per 100 M1 spikes and M2 chlorophyll mutation frequency. The spectrum of chlorophyll mutations was also broadened in the presence of these antioxidants.