Abstract: b-aminobutyric acid (BABA) is a non-protein amino acid that confers wide-rangingprotection in a number of plant families against a variety of plant pathogens, nematodes andinsect herbivores. This paper aimed to clarify some of the conditions under which application ofBABA to a host plant inhibits the performance of aphids. With whole plants, application ofBABA by spraying or dipping foliage had no effect on aphid performance, whereas applicationas a root drench caused a reduction in growth of a number aphid species developing on a range ofhost plants. This suppression was not observed when γ-aminobutyric acid was applied,suggesting the effect is isomer specific. Aphid growth was also reduced on detached leaveswhere the cut end of the petiole was immersed in BABA-solution, indicating that the plant didnot need to be intact for BABA-induced inhibition to occur. Adult aphids maintained on BABAtreatedplants exhibited reduced nymph production after 4-5 days. The findings indicate thatBABA-induced inhibition of aphids is a very general effect, occurring in all plant species so fartested, against all aphid species, genotypes and life stages.