Piridoxilate is a conjugation product of pyridoxine and glyoxylic acid in which pyridoxine is supposed to facilitate in vivo transformation of glyoxylic acid to glycine rather than to oxalic acid. The protective action of piridoxilate against hypoxia and metabolic inhibition of the myocardium was confirmed in the experiments on the canine heart-lung preparation using the redox potential of the myocardium and the pyridine nucleotide fluorescence of the heart as indices of cellular energy metabolism. The protective action of piridoxilate against hypoxia which may be attributable to rearrangement of the myocardial metabolism. Piridoxilate did not induce any significant changes in objective and subjective sleep variables. Long-term treatment with piridoxilate may result in overproduction of oxalic acid and in calcium oxalate nephrolithiasis. Piridoxilate should be added to the list of chemicals responsible for chronic oxalate nephropathy.