Xylem monoterpene composition was determined for 489 trees in eight plots located in areas in Western United States usually assigned to Pinus contorta var. latifolia Engelm. and var. murrayana (Grev.& Balf.) Engelm. Slight variation was found between plots of var. murrayana; larger variation was found within and between plots of var. latifolia. Highly significant differences were found between plots of the two varieties in average composition and individual tree types of composition. Four terpenes--α-pinene, -pinene, 3-carene, and -phellandrene--were the most variable both within and between plots. Forest Sci. 29:333-340.