Abstract : Galectins belong to the family of glycan-binding proteins, defined by at least one conserved carbohydrate-recognition domain with a highly conserved amino acid sequence and affinity for beta galactosides. They all possess a tryptophan residue in the carbohydrate binding site that forms hydrophobic contacts with the carbohydrate ligands. Site directed mutagenesis experiments have shown that this conserved aromatic residue plays a key role in the interaction. We have studied the interaction between the corresponding human Galectin-1 in silico mutants and different carbohydrate ligands using molecular dynamics in explicit solvent. The results confirm the importance of the conserved tryptophan residue in the affinity of the ligand and gives further insights into the mode of interaction between lactose derivatives and human Galectin-1.