Collagen fragments of molecular weights ranging from 700 to 3500 were prepared and allowed to react with hexyl and lauryl aldehydes in order to obtain derivatives of different hydrophobicities. Lauryl collagen forms, in aqueous solutions, aggregates that have low tendency to interact with phospholipid mono and bilayers, with reduced surface activity but the ability to entrap ANS molecules. The hexyl derivative shows a greater hydrophobicity in terms of surface activity and interaction with lipids but a lower ability to incorporate ANS. Underivatized collagen shows no lipid interaction in any of the experiments.