The presence of sorbitol in a concentration 11 mg/ml in a sample reduces by 68 percent the values of fructose glycine measured by colorimetry with thiobarbituric acid. Such sorbitol concentration has no effect on furfural production and on 5-hydroxymethylfurfural reaction with thiobarbituric acid. Measurements of glycolyzed hemoglobin have demonstrated that sorbitol in concentration 11 mg/ml completely inhibits hydrolysis. This fact should be borne in mind when measuring blood glycosylated hemoglobin by colorimetry with thiobarbituric acid and exclude sorbitol from patients' rations before measurements.