The electrical resistivity of high-density polyethylene (HDPE) loaded with carbon black (CB) blends was evaluated as a function of the blending time and the melt index of HDPE. The relationship between the positive temperature coefficient effect and the room temperature volume resistivity was investigated. The positive temperature coefficient effect and reproducibility were improved significantly when the blending time of HDPE and CB was comparatively long. The effects of Co-60 gamma-ray and electron beam irradiation on the positive and negative temperature coefficient behavior of the blends were studied. The effect of thermal aging on the volume resistivity was studied to ascertain the structural stability. (C)AV6 2002 John Wiley Sons, Inc.