Abstract: Cystamine derivatives of the formula: ##STR1## [wherein n represents 2 or 3, R.sup.1 and R.sup.2 each represents a hydrogen atom, or an alkyl group optionally substituted by a hydroxy, amino, alkylamino or dialkylamino group, or represents a cycloalkyl or aryl group, and X.sup.1 represents a group selected from the formulae .dbd.N--CN, .dbd.N--NO.sub.2, .dbd.N--COR.sup.3, .dbd.N--COOR.sup.3, .dbd.N--NH--CONH.sub.2, .dbd.N--SO.sub.2 R.sup.3, .dbd.CH--NO.sub.2, .dbd.CH--SO.sub.2 R.sup.3, .dbd.C(CN).sub.2, .dbd.C(CN)COOR.sup.3 and .dbd.C(CN)CONH.sub.2 (wherein R.sup.3 represents an alkyl or aryl group), or R.sup.1 represents a hydrogen atom, R.sup.2 represents an alkyl group optionally substituted by a hydroxy, amino, alkylamino or dialkylamino group, or represents a cycloalkyl or aryl group and X.sup.1 represents an oxygen or sulphur atom] have been found to be useful in the promotion of the growth of non-human animals including birds.