Adhesion to the glycosylated surface of eukaryotic cells, mediated by lectins for example, plays an important role in inflammation and other cellular processes of living organisms. To elucidate the mechanisms involved in the adhesion to cell surfaces and their biological consequences, the investigation of the molecular interactions between carbohydrate recognition domains of lectins and their ligands is of relevance. In this work, we have selected the photoaffinity labeling technique for the exploration of the ligand binding to mannosespecific lectins, particularly the α-mannose-specific adhesin FimH, which is expressed at the tips of type 1 fimbriae of Escherichia coli bacteria. We have designed and synthesized a series of mannosides and glycopeptides derived thereof that are equipped with a photoactive functional group. It was our goal to compare the properties and labeling potencies of different types of photolabile residues, and therefore, photo-