Radiometric assays revealed that thiamine deficiency in rats to whom hydroxythiamine was administered in variable doses, is concomitant with activation of gluconeogenesis from pyruvate in liver tissue. The most probable mechanism of this effect is the cAMP-dependent activation of key enzymes of intracellular glucose synthesis. This process is facilitated by the diminution of the ratio of free forms of NAD+ and NADPH in the cytoplasm.