This report describes the isolation of a cDNA for the rat glucagon receptor by using the glucagon-like peptide 1 receptor cDNA as a probe. Northern blot analysis using the cDNA clone showed that the message encoding the receptor is approximately 2.3 kb in size and is expressed only in liver and kidney among seven tissues tested. To study how glucagon receptor expression is regulated in vivo, the levels of hepatic glucagon receptor mRNA were measured in diabetic mouse model, db/db and control (db/+) mice. Interestingly, the receptor mRNA levels were similar between diabetic and control mice. In contrast, the number of hepatic glucagon receptors in diabetic mice measured by binding assays was significantly higher than that found in normal mice. These results suggest that the major regulation in hepatic glucagon receptor expression in vivo is at the posttranscriptional level.