Abstract: Described herein are peptide derivatives of the formula R.sup.1 NH--CO--Q--C(O)--NR.sup.2 --CH[CH.sub.2 C(O)--Y]--C(O)--NH--CH[CR.sup.3 (R.sup.4)--COOH]--C(W)--NH--CHR.sup.5 --Z wherein R.sup.1 is an optionally substituted alkyl or optionally substituted phenylalkyl, R.sup.2 is hydrogen or alkyl, R.sup.3 and R.sup.4 each independently is hydrogen or alkyl, or R.sup.3 and R.sup.4 are joined to form a cycloalkyl. R.sup.5 is alkyl, cycloalkyl or (cycloalkyl)alkyl, Q is a divalent radical, for example, --CH.sub.2 CH.sub.2 --, --CH.dbd.CH-- or 1,2-cyclohexanediyl, which serves as a two carbon spacer. W is oxo or thioxo, Y is, for example, an alkoxy or a monosubstituted or disubsdtuted ammo, and Z is a terminal unit, for example, hydrogen, COOH or CH.sub.2 OH. The derivatives are useful for treating herpes infections.