The major auxin of Scots pine (Pinus silvestris L.) which is transported basipetally into agar strips from the cambial region of the stem was quantified by the Went Avena coleoptile curvature assay before and after reversed phase C18 high performance liquid chromatography (HPIL), and then identified by full spectrum gas chromatography-mass spectrometry (GC-MS) as indole-3-acetic acid (IAA). The IAA was subsequently quantified by GC-MS-selected ion monitoring (SIM) using an internal stadard of [13C]-(C6)-IAA. The amount of IAA collected into 22-millimeter long agar strips during 10 minutes of contact with the stem cambial region was estimated by GC-MS-SIM and the Went bioassay to be 2.3 and 2.1 nanogrs- per strip, respectively. The GC-MS technique thus confirmed the results obtained by the Went curvature assay. The Arem curature assay revealed the presence of at least one other, more polar (based on HPLC retention time) auxin that diffused into the agar strips with the IAA. Its bioactivity was only 5% of the UIA fraction. Its HPLC retention time was earlier than IAA-glucoside, IAA-aspartate, or IAAglycine, but the same as IAA-inositol. No sigifnt amounts of inhibitors or synergists of IAA activity on the Arena assay were found in extracts corresponding to one or five strips of agar. Thus, the direct bioassay of the agr strips immediately after their removal from the cambial region of P. silhestris stem sections reflects the concentration of the native IAA. For both P. silhestris and lodgepole pine (Pings contorta) a wavelike pattern of auxin stimulation of Arena curvature was found in apr strips exposed for oaly 10 minutes to the basal ends of an axial series of 6 millimeter long sections from the cambisl region of the stem. This wavelike pattern was subsequently confirmed for P. contota both by A4ena curvature assay and by GC-MS-SIM of HPLC fractions at the retention time of [3H]IAA. The wavelike pattern of auxin diffuing from the cambial region of Pinus has thus been determined to consist primarily of IAA and this pattern has now been quantitated using both the Went APena curvature assay and GC-MS-SIM with [13C]-C6-IAA as an internal standard.