Ex-situ protection of donor organs for transplantation with initial cold perfusion is routinely used. The superiority of the Histidin-Tryptophyn-Ketoglutarate solution (HTK) has been demonstrated in animal models and clinical use. On the other hand, nephron sparing surgery for surgical or functional solitary kidneys has been proved effective for many years. Due to widely used ultrasound and computerized tomography, the incidence of small renal tumors has increased. Therefore, new concepts in conservative renal surgery are gaining more popularity. In this study we report about 11 patients with renal masses in a functional solitary kidney. For the first time, all enucleations were performed with continuous in-situ perfusion with HTK-solution. Despite extensive tumors with central extension, complete in-situ tumor resection and kidney reconstruction were possible. There were no intraoperative complications. Postoperatively, one kidney was lost secondary to renal artery embolism. Urine production started within one hour postoperatively in all cases. No further patient needs haemodialysis. Postoperatively, renal function was largely unchanged except for a transient minor elevation of the serum creatinine. There were no changes of serum creatinine. There were no changes of serum electrolytes and no cardiac failures under HTK. The indication, the surgical procédures and the first clinical results of continuous in-situ perfusion with HTK-solution for conservative renal surgery are presented.