The fructosamine normal range was established from a collective of 90 healthy individuals as 219-285 mumol/l (+/- 2s; mean 240 mumol/l). From a group of 10 diabetics day profiles of glucose, protein, albumin, and fructosamine were recorded by measuring these parameters three times per day at 8.00, 11.30, and 15.00. The fructosamine concentration was essentially constant also when related to protein or albumin. Fructosamine, HbAlc, CK, and CK-MB were determined from 12 diabetics with fresh myocard infarct (7 diabetics, 5 non-diabetics). Surprisingly, diabetics as well as non-diabetics manifested high fructosamine concentrations. The origin of the fructosamine increase with non-diabetic myocard infarct patients is not yet known. Possibly the acute metabolic disorder plays an important role. An influence of fibrinogen on fructosamine is also conceivable. Additional investigations, including therapy of lysis, will be carried on. The stability of the fructosamine was examined by storing 50 sera (fructosamine 295-491 mumol/l, glucose 180-279 mg/dl) at different temperatures (+ 25 degrees C, + 4 degrees C, - 20 degrees C). At - 20 degrees C and + 4 degrees C fructosamine increases by up to 2% in 24 hours. At + 25 degrees C a 6% increase in fructosamine was observed within the same observation period.