The specificity of compensation by Brassica napus L. and Sinapis alba L. was investigated for herbivory by three biting and chewing herbivores: a small adult Coleoptera and a small and a large Lepidoptera larva. Phyllotreta cruciferae (Goeze) damaged the apical meristem and its defoliation of cotyledons was highly dispersed; the defoliation of Plutella xylostella L. was moderately dispersed over cotyledons; and Mamestra configurata (Walker) defoliated large contiguous areas of cotyledons. These types of herbivory were simulated in the field, and postdefoliation compensation by the plants was quantified: leaf length, relative growth rate of foliage, and seed production were measured. Plants were unable to compensate completely for meristem defoliation combined with highly dispersed cotyledon defoliation, and compensated better as cotyledon defoliation became less dispersed. Because compensatory responses to artificial defoliation were similar to and usually indistinguishable from those of insect herbivory, we conclude that the specificity of compensation is caused by the type of defoliation. Other interaction-specific processes such as transfer of growth-affecting chemicals from insect to plant need not be invoked. Sinapis alba compensated for defoliation better than B. napus because of inherent differences in compensatory responses, not because insects defoliate the two plant species differently.