The present invention provides a peptide, peptidomimetic or amino acid derivative having a net positive charge of at least +2 and incorporating a disubstituted &bgr； amino acid, each of the substituting groups in the &bgr； amino acid, which may be the same or different, comprises at least (7) non-hydrogen atoms, is lipophilic and has at least one cyclic group, one or more cyclic groups within a substituting group may be linked or fused to one or more cyclic groups within the other substituting group and where cyclic groups are fused in this way the combined total number of non-hydrogen atoms for the two substituting groups is at least (12), for use as a cytolytic therapeutic agent； as well as non therapeutic uses of these molecules and certain defined novel compounds from within this definition.
