An ethylene polymerization process is disclosed. Ethylene is polymerized in two slurry reaction zones with a C.sub.6-C.sub.10 alpha-olefin in the presence of a single-site catalyst capable of making a high molecular weight polyolefin. The process yields medium density and linear low density polyethylene having a bimodal molecular weight distribution and a melt index from about 0.10 to about 0.80. Films from the polyethylene have superior impact properties.