Chronic surgical explantation of the left rat kidney out of the abdominal cavity under the flank skin enabled easy access to the organ and ipsilateral urine collection under light chloralose anesthesia without virtually any surgical intervention. The glomerular filtration rate, urine flow and osmolality, sodium excretion, and medullary tissue hypertonicity were similar in the explanted and in the contralateral kidney, whereas p-aminohippurate clearance was 14% lower. The function of the explanted kidney was also compared with that of the kidney acutely exposed in rats under thiobutabarbital anesthesia and rendered euvolemic by isoncotic albumin infusion. Again, in both preparations renal function was comparable except that over time urine osmolality remained stable in the former and fell from 1,385 +/- 195 to 835 +/- 167 mosmol/kgH2O (P < 0.02) in the latter, indicating deterioration of urine concentration. Laser-Doppler probes could be easily applied in the explanted kidney to measure cortical and medullary blood flow. The new experimental model offers some advantages, both over studies using conscious rats and over experiments involving deep anesthesia and acute surgery.