Due to increasing availability of methyl alcohol, methanol poisoning becomes more common. Consumption of even relatively small amounts can lead to very serious consequences, including irreversible damage to the eye and death. Quickly implemented proper treatment can alleviate the course of poisoning. Since the victims of poisoning often come to medical facilities unconscious, unresponsive, with unknown or incomplete medical history, it is crucial, both for toxicologists and emergency physicians, to consider the possibility of methanol or ethylene glycol poisoning. It is important to be able to recognize the symptoms of such a poisoning and to order appropriate laboratory tests, especially arterial blood gas and if necessary serum concentrations of methanol and ethylene glycol. The article discusses the course of methanol poisoning, various diagnostic methods of detecting methyl alcohol and factors that affect the methanol concentration in serum. Two clinical cases of patients with non-respiratory acidosis and hyperglycemia, the presence of methanol determined by spectrophotometric method and no methanol intake in anamnesis were also presented. We are considering the possibility of false positive results of methanol determination in the course of diabetic ketoacidosis and significant hyperglycemia.