Nonmodified and corona-activated conifer wood flour was evaluated as filler to nitrile butadiene rubber (NBR) compounds containing different amounts of phenol-formaldehyde resin (PFAR) by studying the cure characteristics and the mechanical properties of the filled compounds. It was found that the PFAR affects considerably the cure characteristics and the mechanical properties of the wood flour-filled NBR compounds due to a presumable action as an interface interactions modifier. Acting as an antiaging agent it improves also their thermal-oxidative stability. The optimal amount of PFAR regarding the cure characteristics and mechanical parameters is of 15 phr/100 phr wood flour. The addition of PFAR just before the wood flour is preferable because of both its better homogenization in the rubber matrix and its lower adsorption by the wood flour, leading to an improvement of the mechanical properties of the wood flour-filled NBR compounds. The replacement of nonmodified wood flour by corona-activated wood flour leads to additional increase of the mechanical parameters without significant affect of the optimum cure time, aging resistance, and water adsorption. (C) 2004 Wiley Periodicals, Inc.