The callus obtained from the growing plant of Ononis arvensis L. was cultivated on the Murashige-Skoog (MS) medium containing a-naphtylacetic acid (NAA) in concentration of 10 mg/1 or 2,4-dichlorphenoxyacetic acid (2,4-D) in concentration of 1 mg/l. It has been found out that it should be taken 0.5-1.5 g of the callus, for starting a long-term cultivation. In this case the duration of the lag phase is cut down. The MS medium containing NAA caused a higher increase of the biomass (the higher percentage rate of the fresh mass increase - 1500) in comparison with the MS medium with 2,4-D (the rate of the fresh mass increase - 250). Additionaly, the higher flavonoids content (0.10%) was noticed in the callus cultivated on the MS medium containing NAA at the steady light (this result refers to the 25 - 40 day callus).In the same time the tissue culture cultivated of the day-light period was still is the phase of the intensive growth. The number of passages play also an important role in the biosynthesis of flavonoids. During the first passages the flavonoids content reached the value of 0.20%, after ten passages - 0.15%, whereas after twenty passages - only 0.05%.