Two peroxidase (POD) cDNAs, anionic (swpa1) and neutral (swpn1) POD derived from suspension cultures of sweet potato (Ipomoea batatas), were used to express high levels in transgenic plants. Two sweet potato PODs were overproduced in two cultivars of transformed tobacco (Nicotiana tabacum) plants, cv. Bel W3 and cv. Samsun by introducing a chimetic gene composed of the cauliflower mosaic virus 35S promoter and POD cDNA. Young fully expanded leaves of transgenic plants of both cultivars showed higher POD activity than those of nontransgenic plants. Bel W3 transgenic plants Carrying anionic POD had total POD activity ca five times higher than control plants. However, no significant differences were observed in superoxide dismutase activity between transgenic and nontransgenic plants. Transgenic Bel W3 and Samsun tobacco plants with either anionic or neutral POD isoenzyme did not show distinctive phenotypes compared with untransformed plants.