BACKGROUND Leptin, is produced by adipose tissue and is presumed to be involved in the regulation of appetite and energy balance. The kidneys are involved in the inactivation of circulating leptin, and elevated plasma leptin concentrations were reported in uraemic patients. Finally, glucocorticosteroids as used in transplanted patients stimulate leptin secretion. METHODS The present study aimed to asses the relationship between plasma leptin concentration and kidney graft function in the early post-transplant period. We studied 40 successfully transplanted haemodialysed uraemic patients (27 males, 13 females, mean age 34.3 +/- 1.6 years, mean body mass index 22.5 +/- 0.5 kg/m2). The circadian rhythm of leptinaemia and insulinaemia was assessed twice: 2-4 days after kidney transplantation and 1 day before discharge from the hospital when graft function was good. Plasma leptin concentration was measured at 8 am, 4 pm, and 12 pm. The control group consisted of 21 healthy subjects (13 males, 8 females, mean age 39.4+/-2.5 years, mean body mass index 24.1 +/-0.7 kg/m2). RESULTS Before kidney transplantation, patients had elevated plasma leptin and insulin levels. A positive correlation was found between BMI and leptinaemia and BMI and insulinaemia, respectively. An inverse relationship was found between leptinaemia and age. Successful kidney transplantation was followed by a significant decline of leptinaemia i.e. from 21.5 +/- 0.1 vs 7.1 +/- 1.3 ng/ml. Kidney transplantation did not influence the circadian rhythm of leptinaemia. CONCLUSIONS Leptinaemia was not related to the excretory graft function or immunosuppression. In addition to renal excretory function, other factors must be involved in the post-transplant decline of leptinaemia.