The paper reviews the development of epoxide-resin casting systems for the potting of electronic components and gives the results of some long-term investigations of the effect of various resin formulations on component values.The first part of the paper deals with the chemical aspects of the reliability of resin-cast components, together with an assessment of the results of some long-term chemical immersion tests. The second part covers the drift of component values during temperature cycling and storage, with particular reference to grade I high-stability resistors.