A compound of formula I: wherein R1 is a straight or branched alkyl group containing 8 to 16 carbon atoms at the 2- or 3-position of the morpholino ring, and R2 is a straight or branched alkyl group containing 2 to 10 carbon atoms, substituted with a hydroxy group except in the alpha-position, the sum of the carbon atoms in the groups R1 and R2 being at least 10 and preferably 10 to 20, is used to prevent biofilm formation on a surface. The compounds are particularly useful as coatings or treatments for medical devices, including stents, catheters and wire guides.