Ethylene enhanced the levels of peroxidases in the roots, stems, leaves, and cotyledons of 2-week-old cucumber Cucumis sativus cv Poinsett 76 seedlings. Antibodies to the isoelectric point (pi) 9 and pi 4 isoenzymes were used in a radial immunodiffusion assay to demonstrate that ethylene induced similar peroxidases in other cultivars of C. sativus, other species of Cucumis and other genera of Cucurbitaceae. Examination of ethylene-induced peroxidases, using isoelectric focusing gels, demonstrated the presence of a series of other peroxidases, mostly slightly acidic, whose isoelectric focusing pH was approximately 6. These pi 6 peroxidases were partially purified on a cation exchange column. Ouchterlony double diffusion gels indicated that these proteins cross-reacted with antibodies to both the pi 9 and pi 4 peroxidase. The data presented here suggest that the induction of peroxidase isoenzymes during ethyleneinduced senescence is a common response in this family of plants. In addition, antibody and isoelectric focusing studies indicate that both acidic and basic peroxidase are highly conserved in members of this family.