Abstract: Ganglioside lactam analogue derivatives of general formula (I) in which A is a sialic acid residue of formula (II) which is bound via the dashed line in the 2-position; and in which Z.sup.1 is --OH or a group --NHX.sup.1, and Y.sup.30 is --CH.sub.3 or --CH.sub.2 OH; X.sup.1 and Y.sup.1 together form a bond and Y.sup.2 is --OH or a group OR.sup.20, or X.sup.1 and Y.sup.2 together form a bond and Y.sup.1 is --OH or --NHAc; Y.sup.3 is --OH or a group --OR.sup.20 ; R.sup.1 is H or a sialic acid residue of formula (III) which is bound via the dashed line in the 2-position; and in which Z.sup.2 is --OH or a group --NHX.sup.2, and Y.sup.30 is as defined above; X.sup.2 and Y.sup.10 together form a bond and Y.sup.20 is --OH, or X.sup.2 and Y.sup.20 together form a bond and Y.sup.10 is --OH; with the provisos that when R.sup.1 is H, then Z.sup.1 is --NHX.sup.1, and that when R.sup.1 is a sialic acid residue of formula (III), then at least one of Z.sup.1 and Z.sup.2 is different from --OH; R.sup.