abstract uracil herbicide residues were studied in the medicinal plant lemon balm (melissa officinalis l. c.v. citra) grown under standard agrochemical conditions. the residues from the uracil herbicides bromacil, lenacil, and terbacil were determined at selected phases of flower development. in addition the main components of the m. officinalis oil were determined by gc/ms at the same stages of development such as bud set, at the beginning of bloom, and at full bloom. tlc on silica gel with selective biochemical detection was used for the determination of herbicide residues in the plant material. it was found that the sample of plant material harvested in full bloom state contained 0.007 mg/kg of bromacil residue, and 0.005 mg/kg of lenacil and terbacil residues. the application of the herbicide at a rate of 2 kg/ha did not affect the quality of the treated plant.