The work was aimed to study the changes in the content of cyanogenic glycosides in forage biomass of birds’-foot trefoil grown alone and in mixtures with subterranean clover, cocksfoot and tall fescue. The content of cyanogenic glycosides was determined in leaves, stems and flowers in fresh plant. Cyanogenic glycosides content in stems of birds’-foot trefoil was found 38.40 mg HCN/100 g DM, in leaves 90.39 mg HCN/100 g DM and in flowers 173.60 mg HCN/100 g DM, respectively. The content of cyanogenic glycosides in plants of three subclover subspecies was found very low, i.e. Trifolium subterraneum ssp. subterraneum (2.84 mg HCN/100 g DM), Trifolium subterraneum ssp. brachycalicinum (3.18 mg HCN/100 g DM), Trifolium subterraneum ssp. yaninicum (7.87 mg HCN/100 g DM). In the mixtures of birds’-foot trefoil with subclover the content of cyanogenic glycosides increased in both components compared to their pure grown – in birds’-foot trefoil from 8.8% to 19.9%, and in subclover from 10.7 to 54.4%. The content of cyanogenic glycosides in birds‘-foot trefoil increased by 6.0% in mixtures with tall fescue and with 17.9% in mixtures with cocksfoot. The higher proportion of subclover in the mixtures with birds’-foot trefoil decreased the cyanogenic glycosides content.