The activity of adenosine kinase is significantly impaired in tissues of diabetic rat. Changes in the activity of adenosine kinase were accompanied by alterations in its mRNA and protein level. These changes depended on insulin level and were not related to glucose level. During the first 7 h after insulin treatment the level of adenosine kinase mRNA, protein and enzymatic activity in kidneys, liver and heart returned to normal values. The observed relation between insulin and adenosine kinase expression level may suggest that insulin increases the rate of adenosine kinase gene transcription. Decreased activity of adenosine kinase was associated with elevated level of adenosine in diabetic tissues. On the 10th day after the STZ treatment there was a 3.5 and 2-fold increase in adenosine content in heart and liver, respectively. On the other hand, in diabetic kidney adenosine level was elevated only by 20%. Administration of insulin to diabetic rats resulted in a drop of adenosine to the level seen in normal heart and liver whereas, in kidneys the adenosine content was 50% lower than that observed under normal conditions. The time-dependent coarse of changes in adenosine level was different from that observed for adenosine kinase activity, what may suggest that other factors, possibly nucleoside transporters are also important for controlling adenosine level in the cell.