Abstract: Cyclosporins having anti-bacterial activity useful as immuno suppressive and anti-inflammatory agents are provided, such as undecapeptides of the formula (I) ##STR1## in which A.sub.1 is either derived from 2-carboxyazetidine, 2-carboxypyrrolidine or 2-carboxypiperidine, or is an amino acid residue ##STR2## wherein n is 0, 1 or 2, X represents an amino, methylamino, mercapto or hydroxy group, R represents hydrogen or an acyclic aliphatic hydrocarbon group and R' represents hydrogen or methyl; A.sub.2 is an amino acid residue ##STR3## wherein R.sub.1 is an acyclic aliphatic hydrogen group optionally substituted at the C.sub.1 position of the group R.sub.1 by an amino, methylamino, mercapto or hydroxy group, but with the proviso that when R.sub.1 is a group of less than four carbon atoms then A.sub.1 is a heterocyclic amino acid residue or is an amino acid residue --R'N--CH(CHR(CH.sub.2).sub.

Abstract: Of therapeutic value in various contexts in which the cyclosporins are used, for example as anti-bacterial agents and particularly as immunosuppressive and anti-inflammatory agents, are acyclic undecapeptides having the formula (I)H--A.sub.1 --A.sub.2 --A.sub.3 --A.sub.4 --A.sub.5 --A.sub.6 --A.sub.7 --A.sub.8 --A.sub.9 --A.sub.10 --A.sub.11 --OH (I)in which A1 is either derived from 2-carboxyazetidine, 2-carboxypyrrolidine or 2-carboxypiperidine, which may optionally be substituted on a ring carbon atom other than that at position 2 by an amino, methylamino, mercapto or hydroxy group and/or by an acyclic aliphatic hydrocarbon group, or is an amino acid residue ##STR1## wherein n is 0, 1 or 2, X represents an amino, methylamino, mercapto or hydroxy group, R represents hydrogen or an acyclic aliphatic hydrocarbon group and R' represents hydrogen or a methyl group; A2 is an amino acid residue ##STR2## wherein R.sub.