Biochemical processes involved in hypersensitive plant cell death were explored with purified harpin and inhibitors of eukaryotic metabolic processes. alpha-Amanitin, cycloheximide, vanadate, lanthanum, and WIN50805 prevented or delayed the HR elicited by harpin in tobacco leaves; k-252a and staurosporine had no effect. In contrast, the K+/H+ exchange response of tobacco cell cultures elicited by harpin was inhibited by only lanthanum and k-252a.