Kernels of the maize inbred FR27rhm were cultured on various media to determine if the treatments would alter the frequency of formation of regenerable callus (induction frequency) by embryos excised from the kernels when they were placed on callus induction medium. The addition of 60 μM dicamba (3,6-dichloro-o-anisic acid) to the kernel culture medium resulted in an induction frequency of 27-38% compared to 0% for controls on standard kernel culture medium. Embryos excised from dicamba-treated kernels also showed in-ovule callus-like tissue proliferation. The increased induction frequency and the callus-like tissue proliferation could also be produced by injecting the ears of field grown FR27rhm plants, 3-d post pollination, with 1.08 μmoles of dicamba. The results indicate that treatment of the developing ear with dicamba, in vivo or the developing kernel in vitro, may be an effective means to increase the frequency of regenerable callus induction from recalcitrant maize genotypes, such as the B73 derivative FR27rhm.