Immunoreactive insulin level (IRI) in haemolyzed (HE) of normal fasting subjects was 49.2 +/- 3.5 microU/ml. It was approximately 5 times higher compared within the plasma levels of the same subjects. Recovery and dilution tests for insulin in HE were positive. After an intravenous glucose load IRI in HE decreased to 14.3 +/- 3.6 microU/ml with 5 minutes and was low during 1 hour after glucose administration. Authors results suggest the presence of insulin in human erythrocytes and it release from erythrocytes during the first phase after glucose loading.