Several relationships between tensile strength and some lumber characteristics that can be measured nondestructively are evaluated. From 72 to 83 percent of the variation in tensile strength of several hundred southern pine 2- by 4- and 2- by 8-inch specimens was accounted for by various linear combinations of strength ratio of knots, stiffness, slope of grain, and specific gravity. Strength ratio of knots and stiffness were the most significant variables. Evaluated in conjunction with other variables, stiffness measured over a 4-foot span improved the coefficient of determination of 2 by 4's by about 0.05 compared to stiffness measured over a 15-foot span; three methods to determine strength ratio of knots gave coefficients of determination that differed by a maximum of 0.08. A method for estimating lower 5 percent exclusion values for tensile strength is also presented. (Author).