Often, well-controlled plasma glucose levels but high hemoglobin A(1c) levels have been observed at prehemodialysis in diabetic patients. The present study aimed to evaluate this difference between fasting glucose and hemoglobin A(1c) levels. We investigated hemodialysis-induced alterations in the plasma glucose and insulin levels. Based on their glycemic control level at inclusion, subjects were divided into poor control (hemoglobin A(1c)> or =7.0%; n = 8) and good control groups (hemoglobin A(1c) <7.0%; n = 8). We measured their plasma glucose and immunoreactive insulin levels at arterial and venous sites at three time points (predialysis, 2 h and 4 h after starting dialysis); we also studied their daily plasma glucose profiles. In both the groups, the V-site plasma glucose and immunoreactive insulin levels were significantly decreased compared to the A-site levels at each time point. The A-site plasma immunoreactive insulin levels 4 h after dialysis were significantly decreased compared to the levels 2 h after dialysis. Comparison between hemodialysis and non-hemodialysis days revealed that the plasma glucose levels decreased significantly during hemodialysis and significantly increased between predinner and bedtime in the poor control group. The present study confirmed that hemodialysis decreased the plasma glucose and immunoreactive insulin levels. In the poor control group, hyperglycemia appeared posthemodialysis; this was attributed partly to the hemodialysis-induced decrease in the plasma immunoreactive insulin levels. These results suggest that although diet therapy has been effective in diabetic hemodialysis patients, hemodialysis caused hyperglycemia by absolute or relative plasma immunoreactive insulin deficiency.