This paper reviews literature dealing with the measurement of oleoresin exudation pressure and the flow of resin from pine resin duct systems, with special reference to assessing tree resistance to bark beetle attack. The adequacy of a modification of Poiseuille's equation to predict resin flow is questioned, and resin pressure is judged to be an inadequate substitute for direct measurement of resin flow and estimation of tree resistance to bark beetle attack. Although direct measurement of resin flow is considered to be a superior method of eshating the relative resistance of trees to attack, it probably is not a totally satisfactory method for estimating resin flow, i.e., resistance to attack, associated with the progressive wounding done by bark beetles in their attempts to establish egg galleries. Multidisciplinary, integrated studies are needed to improve understanding of tree-bark beetle interactions.