Abstract: The present invention relates compounds of the formula: oligosaccharide-spacer-(GpIIb/IIIa antagonist), wherein the oligosaccharide is a negatively charged oligosaccharide residue comprising four to twenty five monosaccharide units, the charge being compensated by positively charged counterions, and wherein the oligosaccharide residue is derived from an oligosaccharide which has (AT-III mediated) anti-Xa activity per se; the spacer is a bond or an essentially pharmacologically inactive linking residue; the GpIIb/IIIa antagonist is a residue mimicking the RGD and/or K(QA)GD fragment of fibrinogen, comprising a carboxylate moiety and a basic moiety located within the residue at a distance of 10-20 ? from each other; or a pharmaceutically acceptable salt thereof or a prodrug or a solvate thereof; wherein the compound of formula I further comprises at least one covalent bond with a biotin label or an analogue thereof.