A cyclic tetrapeptide compound of the formula (I): wherein R.sub.1 is hydrogen; R.sub.2 is lower alkyl, aryl, optionally substituted ar(lower)alkyl, heterocyclic(lower)alkyl, cyclo(lower)alkyl(lower)alkyl, lower alkylcarbamoyl(lower)alkyl or arylcarbamoyl(lower)alkyl; R.sub.3 and R.sub.4 are each independently hydrogen, lower alkyl, optionally substituted ar(lower)alkyl, optionally substituted heterocyclic(lower)alkyl or cyclo(lower)alkyl(lower)alkyl, or R.sub.3 and R.sub.4 are linked together to form lower alkylene or condensed ring, or one of R.sub.3 and R.sub.4 is linked to the adjacent nitrogen atom to form a ring; R.sub.5 is lower alkylene or lower alkenylene, Y is [wherein R.sub.Y1 is hydrogen, halogen or optionally protected hydroxy, R.sub.Y2 is hydrogen, halogen, lower alkyl or phenyl, and R.sub.Y3 is hydrogen or lower alkyl]; R.sub.8 is hydrogen or lower alkyl; and n is an integer of 1 or 2, or a salt thereof.