Protein and peroxidase banding patterns were obtained by disc electrophoresis of leaf extracts from flowering olants of Petunia axillaris (Lam.) B.S.P., P. inflata R. Fries, P. violacea Lindl., P. parodii W.C.S., and 11 cultivars of P. hybrida Hort. These molecular markers were studied to determine taxonomic relationships among the species and to relate these to the synthesis of P. hybrida. A total of 11 peroxidase isoenzymes were resolved from the species and two additional isoenzymes from the cultivars. Petunia axillaris and P. inflata had identical banding patterns with seven sites of enzyme activity resolved; P. violacea had 10 bands and P. parodii had seven bands. The peroxidase banding patterns among the cultivars were not identical to those of any of the species; however, the average correlation of the individual species with all of the cultivars was significant at the 5% level: P. axillaris, .74; P. inflata, .73; P. violacea, .52; and P. parodii, .68. Only two peroxidase bands, 4 and 13, were found to be common to all species and cultivars. A total of 48 different protein bands were resolved from the species and cultivars. No two species and/or cultivars possessed identical patterns. Only three protein bands, 2, 8, and 12, were common to all species and cultivars. Petunia axillaris was not significantly correlated with P. inflata, P. violacea, or P. parodii, although the latter three were significantly correlated with each other. Only P. inflata was significantly correlated, on the average, with all of the cultivars. The four species investigated were determined to be closely related taxonomically although properly classified as distinct species. The results indicated that P. axillaris has made a major contribution in the development of P. hybrida. While previous studies have shown that P. violacea may be considered a putative parent of P. hybrida, the present study presents stronger evidence for the implication of P. inflata.