The effects of the solid-acid-catalyst pore size and acidity on polyethylene catalytic cracking were examined with a comparison of the temperature-dependent volatile-product-slate changes when the polymer was cracked with HZSM-5 and HY zeolites and the protonated form of MCM-41. Volatile-product distributions depended on the catalyst acidity and pore size. With HZSM-5, paraffins were detected initially, and olefins were produced at somewhat higher temperatures. Aromatics were formed at temperatures 30-40 degreesC higher than those required for olefin production. Small olefins (C-3-C-5) were the most abundant products when HZSM-5 and MCM-41 catalysts were employed for cracking polyethylene. In contrast, cracking with HY produced primarily paraffin volatile products (C-4-C-8). HY pores were large enough and the acid sites were strong enough to promote disproportionation reactions, which led to the formation of volatile paraffins. Compared with the other catalysts, HZSM-5 with its smaller pores inhibited residue formation and facilitated the production of small alkyl aromatics. Volatile-product variations could be rationalized by a consideration of the combined effects of catalyst acidity and pore size on carbenium ion reaction pathways.