Substantially pure peptides containing between 13 and 20 amino acids, inclusive, having the amino acid sequence: R1-R2-R3-R4-R5-R6-R7-R8-R9-R10-R11-R12-R13-R14-R15-R16-R17-R18-R19-R20-R21-R22-R23, where R1 is Asp or is absent; R2 is Ser or is absent; R3 is His or is absent; R4 is Ala; R5 is Lys, Gln, Arg, or another basic amino acid; R6 is Arg, Gln, Lys, or another basic amino acid; R7 is His, Phe, Tyr, Leu, or another hydrophobic amino acid; R8 is His, Phe, Tyr, Leu, or another hydrophobic amino acid; R9 is Gly, Lys, Arg, or another basic amino acid; R10 is Tyr; R11 is Lys, His, Phe, or another hydrophobic amino acid; R12 is Arg, Gln, Lys, or another basic amino acid; R13 is Lys, Gln, Arg, another basic amino acid, or is absent; R14 is Phe or is absent; R15 is His, Phe, Tyr, Leu, another hydrophobic amino acid, or is absent; R16 is Glu or is absent; R17 is Lys or is absent; R18 is His or is absent; R19 is His or is absent; R20 is Ser or is absent; R21 is His or is absent; R22 is Arg or is absent; and R23 is Gly or is absent; and where Gln cannot simultaneously occupy positions R5, R6, R12, and R13 of the amino acid sequence, as well as pharmaceutical compositions containing these peptides and methods for treating fungal and bacterial infections using these peptides, are disclosed.