Many pharmaceutical drugs arc isolated from plants used in traditional medicines, and new plant-derived pharmaceutical drugs continue to be identified. Relevant to this review, different plant-derived agonists for gammadelta T cells are described that impart effector functions upon distinct subsets of these cells. Recently, plant tannins have been defined as one class of gammadelta T cell agonist and appear to preferentially activate the mucosal population. Mucosal gammadelta T cells function to modulate tissue immune responses and induce epithelium repair. Select tannins, isolated from apple peel, rapidly induce immune gene transcription in gammadelta T cells, leading to cytokinc production and increased responsiveness to secondary signals. Activity of these tannin preparations tracks to the procyanidin fraction, with the procyanidin trimer (C1) having the most robust activity defined to date. The response to the procyanidins is evolutionarily conserved in that responses are seen with human, bovine, and murine gammadelta T cells, although human cells show less selectivity. Procyanidin-induced responses described in this review likely account for the expansion of mucosal gammadelta T cells seen in mice and rats fed soluble extracts of tannins. Use of procyanidins to activate gammadelta T cells may represent a novel approach for the treatment of tissue damage and autoimmune diseases.