Environmental stress crack resistance, ESCR, of several candidate plastics for instrument panels was studied using both constant load and constant strain methods. Poly-carbonate/ABS blends demonstrated significantly better ESCR properties than the polystyrene modified polyphenylene oxide system. The mechanism of failure was followed using SEM microscopy which showed that the load carrying phase was polycarbonate. Furthermore, a fracture mechanics study under dry conditions and in the presence of the aggressive environment was done. The data, based on the critical stress intensity factor in and away from the stress cracking environment, explains the behavior of polycarbonate/ ABS blends relative to the modified polyphenylene oxide system.