A simple and improved dwarf rice (Oryza sativa var Tan-ginbozu) lamina inclination bioassay for brassinosteroids (BRs) was developed based on a previously published method (K Takeno, RP Pharis [1982] Plant Cell Physiol 23: 1275-1281). The assay used 3-day-old intact seedlings, and detection of BR was made more sensitive by synergizing the response to BR with indole-3-acetic acid (IAA). The minimum detectable amount of BR was less than 0.1 nanogram/rice plant (brassinolide equivalents). Purification steps for isolation of BR from tissue scrapings taken from the cambial region of Scots pine (Pinus silverstris) harvested during the period of rapid wood production were guided by this assay. After column chromatography (silica gel and PrepPak C18) and reversed phase Cie high performance liquid chromatography, the biologically active fractions were analyzed by gas chromatography-mass spectrometry (GC-MS) and/or GC-MS-selected ion monitoring. Two BRs, castasterone (major) and brassinolide (minor) were identified. This is the first identification of BR from the cambial region of a conifer.Brassinosteroids (BRs)4 are steroidal hormones that promote plant growth. To date, 28 naturally occurring BRs have been identified in various plant tissues (2,4,5,8,16), ranging from higher plants to a green alga ( 15). In conifers, castasterone (scheme 1, structure 2) and typhasterol (2-deoxycastasterone (scheme 1, structure 3) have been identified in pine pollen