This paper briefly describes four areas of work involved in trying to establish the reliability and limitations of thickfilm materials. One of the most widely used resistor systems, Du Pont 1400, has been extensively examined and long-life stability predictions are made. The possibility of replacing gold conductors with lower cost silver alloys depends critically upon controlling or eliminating silver migration, and the conditions under which migration occurs are described. The replacement of alumina substrates with alternative materials such as enamel steel, polymer board or glass is also reported, and the behaviour of the thick film materials has been found to be generally inferior to those on alumina. The Du Pont CMS nitrogenfireable resistor, conductor and dielectric system has been evaluated and the properties found to be comparable with air-fireable systems.