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A fluorometric procedure was used to study changes in levels of the free and bound forms of the cis and trans isomers of o-hydroxycinnamic acid (o-RCA) associated with drying sweetclover (Melilotus) tissues under various conditions of time and temperature. Leaves, or leaves and stems, of three sweetclover varieties, 'Spanish,' 'Evergreen,' and 'Goldtop,' and two closely related, highly inbred lines (CuCuBB and CuCubb genotypes) were used. Drying temperatures of 30 and 40 C were used most extensively. When dried at 30 C, leaves lost more than half of their bound cis-o-RCA, and a small amount of free cis-o-RCA (coumarin) was produced. In leaves dried at 40 C, up to 90% or more of the bound cis-o-RCA was converted to the free form by the enzyme, β-glucosidase, and little loss of total o-RCA occurred. Thus, levels of free and bound cis-o-RCA were appreciably modified by the drying treatments imposed. Content of trans-o-RCA, on the other hand, was not greatly changed by drying. The results obtained may have application in the drying of leaves of deer's tongue [Trilisa odoratissima (Walt. ex J. F. GmeI.) Cassini], an o-RCA-containing plant used in the tobacco (Nicotiana tabacum L.) industry.