Three cytolytic peptides, termed brevinin-1E, brevinin-2E, and esculentin, were isolated from skin secretions of the European frog Rana esculenta (Simmaco, M., Mignogna, G., Barra, D., and Bossa, F. (1993) FEBS Lett. 324, 159-161). Nucleotide sequence analysis of cDNAs coding for the corresponding precursors revealed that in all of them a single copy of the sequence of the mature peptide is present preceded by a dibasic cleavage site and followed by a stop codon. The signal peptides of these precursors show a clear homology to the corresponding region of the precursor of dermorphin, a neuropeptide occurring in the skin of amphibians of the subfamily Phyllomedusinae. Ten new peptides, ranging in size from 24 to 46 residues, all possessing an intramolecular disulfide bridge located at the carboxyl-terminal end, were isolated from skin secretions of R. esculenta. These peptides can be grouped into four subfamilies on the basis of their distinctive structural and/or functional properties. All of these new peptides have antimicrobial and/or hemolytic activities typical for the respective subfamily. In addition, we demonstrate that esculentin-1 also inhibits the growth of Pseudomonas aeruginosa, Candida albicans, and Saccharomyces cerevisiae.