A slurry process for polymerizing ethylene is disclosed. The process comprises polymerizing ethylene in the presence of an .alpha.-olefin and a catalyst comprising an activator and a supported bridged indeno[1,2-b]indolyl zirconium complex. The process produces polyethylene characterized by good incorporation of the .alpha.-olefin and moderate long-chain branching. The process is capable of forming high molecular weight polyethylene and has good catalyst activity.