The effect of chronic caffeine treatment on lipolysis in rat epididymal adipose tissue was studied. There was a decrease in body weight, epididymal fat pad weight and mean adipocyte diameter in caffeine-treated rats when compared with control rats. No difference in adipocyte triglyceride content or mean adipocyte weight between control and caffeine-treated rats was observed. Lipolysis in adipocytes induced by adenosine deaminase (1 U/ml) decreased by 35 % in caffeine-treated rats. This was accompanied by a 2.5-fold increase in the anti-lipolytic potency of 2-chloroadenosine and an increase of adipocyte adenosine A1 receptor number.