The aim of the present study was to quantify beta(2)-adrenoceptor protein content in adipose tissue during fasting, and to study the relationships between beta(2)-adrenoceptor protein and mRNA levels and changes in metabolites related to lipolysis. Groups of male subjects with a body mass index of <25 kg/m(2) or >30 kg/m(2) fasted for 60 h. Abdominal subcutaneous fat biopsies were analysed for receptor mRNA levels by reverse transcription-PCR-HPLC. The beta(2)-adrenoceptor protein concentration was measured by Western blotting using fluorescence laser scanning for detection. The beta(2)-adrenoceptor protein concentration per cell (on a DNA basis) was higher in obese subjects ( P <0.03). There were highly significant relationships between beta(2)-adrenoceptor protein concentration and both body mass index and waist/hip ratio ( P <0.001 for both). Furthermore, there was an inverse relationship between the receptor protein concentration and the serum beta-hydroxybutyrate level during fasting ( P <0.005). beta(2)-Adrenoceptor protein levels decreased in both groups during fasting, to a similar degree. Basal beta(2)-adrenoceptor mRNA levels were similar in the two groups, but there was a smaller increase in the obese group during fasting ( P <0.03). The increased beta(2)-adrenoceptor protein level in obese subjects is likely to be related to the greater plasma membrane area of their adipocytes. The decrease during fasting may be due to increased binding of noradrenaline and subsequent internalization and degradation of the receptor. Elevated levels of less responsive beta(2)-adrenoceptor protein in obese subjects may contribute to the development of obesity.