In all types of treatment thiamine is susceptible to greatest changes. With hydrothermal treatment (HTT) the losses of thiamine amounted to 5.65-8.50 per cent, depending on its variety. The cooking of unground buckwheat originating from such cereals was attended by further losses of thiamine, within the range of 9.07 up to 14.15 per cent, depending upon the variety of the grain. The loss of thiamine was highest in cooking unground buckwheat originating form raw grain, it being within the range of 16.35 up to 19.14 per cent, also depending on the variety of buckwheat. With different procedures in heat treatment riboflavine displayed a greater stability. The HTT was attended by insignificant losses of riboflavine--from 1.09 to 3.96 per cent. The riboflavine losses were found to be highest during subsequent cooking of unground buckwheat of the "Gloria" variety. When cooking groats of raw buckwheat the riboflavine losses are greater than in the case of the grain subjected to the HTT.