[en] A simple, rapid, precise and relatively inexpensive thin-layer chromatographic method coupled to heterogeneous liquid scintillation counting procedure was used for the quantitation of radioactivity of biologically synthesized (¹⁴C) flavonoids and other phenolic plant constituents. The two flavonoids, namely (¹⁴C) rutin and (¹⁴C) (-) -epicatechin, extracted from the plant Uncaria elliptica Roxb were separated on plastic thin-layer plates coated with silica gel using the two solvent systems : acetonitrile-acetic acid-water (8.5:0.5:1.5) and ethyl acetate-acetic acid-water (3:1:3). The respective spots on the plates that corresponded to the two flavonoids were cut out and eluted with 3 ml aliquots of methanol followed by direct addition of scintillation flour. This method gave 99 +- 2 per cent of the total count indicating the excellent elution procedure. The results were reproducible and showed linearity over the range of 0 - 35000 dpm. The elution efficiency by several other organic solvents were also investigated. (author). 19 refs., 4 tables