The effects of corona-discharge treatment (CDT) of commercial polyethylene (PE) Linear low-density PE (LLDPE) were studied with special emphasis on the heat-seal behavior of treated films. A range of treat levels, representative of those used in industry, was obtained by varying the applied power to a commercial, on-line treater. Film surfaces were characterized by XPS and wetting-tension measurements. The primary effect of CDT on the heat-sealing behavior of LLDPE films is a transition in the failure mode of heat seals from a normal tearing or inseparable bond to a peelable seal. In addition, CDT increases the seal initiation temperature 5-17-degrees-C and decreases the plateau seal strength 5-20% as the treat level, or wetting tension, increases from 31 to 56 dynes/cm. These effects are attributed to cross-linking during corona treatment, which restricts polymer mobility near the surface and limits the extent of interdiffusion and entanglements across the seal interface. Results of heat-sealing studies with electron-beam-irradiated PE, chemically oxidized PE, and CDT polypropylene (PP) provide indirect evidence for the proposed surface cross-linking mechanism. The effect of commercial levels of slip additives on the heat-seal behavior was also investigated.