TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: In the method, the parylene film and the antimicrobial agent are deposited simultaneously on a substrate, or the parylene film is deposited on the substrate prior to introduction of the antimicrobial agent. The method further comprises: depositing parylene on the immobilized antimicrobial agent; dissolving the antimicrobial agent in a carrier solvent prior to immobilization; and pretreating the substrate prior to deposition. Preferred Components: The antimicrobial agent comprises octadecyldimethyl(3-trimethoxysilylpropyl)ammonium chloride or a similar compound. The coating includes: a first layer comprising the parylene material; a second layer deposited on the first layer, where the second layer comprises the parylene coating and the antimicrobial agent; and a third layer comprising the parylene material deposited on the second layer. The coating is applied to a medical device substrate. The first layer has a thickness of 0.5-25 mu m. The second layer has a thickness of 50 Angstrom to 5 mu m. The third layer has a thickness of 0.1-2 mu m. The parylene film or the parylene material comprises: substituted 1,4-dimethyl benzene of formula (I) or 2-chloro-1,4-dimethyl benzene of formula (II); and substituted 1,4-bis-difluoromethyl-benzene of formula (III).n = not defined. EXAMPLE - Octadecyldimethyl(3-trimethoxysilylpropyl)ammonium chloride was heated at an appropriate rate to achieve vaporization while avoiding rapid boiling. The resultant vaporized antimicrobial material was then striked the parylene film surface and became anchored to the parylene film through molecular entanglement, hydrogen bonding or covalent bonding depending on the functional groups present in the desired antimicrobial compound and/or on the parylene film surface. Then the parylene deposition system allowed to return to base pressure, the vacuum was released and the system was allowed to return to room pressure, once deposition of parylene film and the desired antimicrobial compound was complete, to form the antimicrobial parylene coating.