Of 20 solutions tested, diazotized benzidine dihydrochloride, 2-methoxyaniline, and fast blue effectively distinguished the sapwood-heartwood boundary in 27-year-old loblolly pine trees. Sapwood-heartwood boundaries identified by UV scanning corresponded to the results indicated by these 3 chemicals. Sapwood thickness was not constant, but was linearly correlated (r = 0.964) with dbh. Forest Sci. 30:756-760.