Pinus merkusii de Vriese xylem resin composition was determined for 150 individual trees from 11 sites across its natural range in Thailand and for 100 trees sampled from ®ve sites in the Philippines. Turpentine composition for the Thai samples was very dependent on provenance origin and provenance means appeared to follow a southeast-to-northwest pattern of increasing a-pinene (from just over 40% to 80% or more). In most cases, 3-carene was the second most abundant constituent. Tree-to-tree variation was occasionally quite marked and in one provenance two trees contained limonene as the major constituent. In contrast, the turpentine composition between and within Filipino provenances was remarkably consistent: only one tree contained less than 94% a-pinene, and 3-carene was mostly absent or present only in trace amounts; the single, odd tree contained 25% 3-carene. Variation in the resin acid composition was far less marked than was the case for the volatile terpenes. Provenance means were broadly similar for both the Thai and Filipino samples, although there again appeared to be a southeast-to-northwest trend in Thailand, with levopimaric/palustric acid content increasing in that direction, and isopimaric and sandaracopimaric acids both falling. Merkusic acid exhibited the greatest tree-to-tree variation (1±20%).