Composites have been made from single-wall carbon nanotubes in a polyethylene (PE) matrix, in which different methods of preparation were used to disperse the nanotubes. The study includes using either the refined pure nanotubes (P-NT) as the source, or the original silica supported nanotubes (SS-NT). SS-NT contained nanotubes still incorporated in and around the silica as originally grown. Composites were then made by (1) coprecipitation from a suspension of P-NT or SS-NT in a PE solution, or (2) by forming a polymerization catalyst from the SS-NT, and using it to polymerize ethylene, which ruptures and expands the silica as polymer builds LIP ill the pores. Extrusion was also studied as a method of additional dispersion. Nanotubes were found to have a powerful effect on the melt rheology, increasing the low shear viscosity dramatically. Increasing the nanotube concentration also increased the flexural and tensile moduli, decreased the elongation, and increased the electrical conductivity. Consistent trends were observed from all of these diverse properties: SS-NT had a stronger effect than P-NT, and within the SS-NT group the choice of silica type also had a major effect. Polymerization was generally preferred as the method of dispersing the nanotubes. The conductivity, which in some cases was quite high, was found to be pressure sensitive. Conductive NT/PE composites could be molded into films or extruded into other shapes, or comolded with other PE. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 589-601, 2009