Plant compensation may be specific to the defoliation of a particular insect herbivore, or a generalized response to herbivory. These alternate hypotheses were tested by measuring biomass and seed production of Brassica napus L. and Sinapis alba L. in response to 0, 25, or 75% defoliation of seedling plants. The herbivores were adults of Phyllotreta cruciferae (Goeze), larvae of Plutella xylostella L., and larvae of Mamestra configurata (Walker). Although defoliated to the same extent, both B. napus and S. alba compensated most for defoliation by M. configurata and least for defoliation by P. cruciferae. Both plant species compensated better for 25% than for 75% defoliation, and S. alba compensated better than B. napus. Laboratory and field experiments showed similar patterns of compensatory leaf growth, but recovery was more rapid in a controlled environment. Compensation was associated with changes in root biomass that were correlated with foliage biomass, indicating that root-shoot ratios were maintained. Complete recovery of foliage after defoliation did not assure complete recovery of plant fitness. For these three herbivorous insects, compensation by two plant species for defoliation was specific to the insect defoliator, and not a generalized response to herbivory. The compensatory responses of the two plant species explain, in part, the differential impact the three herbivores have on the crops.