Electrically conductive adhesives, such as silver-filled epoxies, are used in many applications where standard soldering or direct metal-to-metal connections are not feasible. Anomalous behavior at these connections has been observed as the development of increasing resistance over time in the absence of mechanical failure between the adhesive and substrate. The results of aging of electrically conductive adhesive joints to aluminum- and gord-metallized substrates show that little change occurs at low humidity under an ambient flow of nitrogen. With increasing humidity and temperature, there is a measurable increase in resistance over time, particularly in the case of aluminum-metallized substrates. Secondary ion mass spectrometry (SIMS)was used to investigate interfacial phenomena that may be responsible for increasing resistance observed in the aluminum-metallized samples exposed to accelerated aging. Preliminary results from this technique indicate the presence of an oxide layer between the adhesive and the metallization layer that is consistent with increasing resistance measured for samples exposed to accelerated aging. The results also support the conclusion that deterioration at the adhesive-aluminum interface, and not degradation in the bulk adhesive, is the primary cause of increasing resistance.