OBJECTIVE: To compare the efficacy of cryoablation and radical nephrectomy for treating implanted VX-2 carcinoma in rabbit kidneys. MATERIALS AND METHODS: A pilot study was conducted using 27 New Zealand white rabbits to assess the natural history of VX-2 carcinoma in the kidney. VX-2 tumour segments (1 mm(3)) were excised from subcutaneous tumours in carrier rabbits and implanted in the left kidney of study rabbits. The tumours were allowed to grow for 6, 7, 8, 9, 10, 14, 18, 21 and 28 days after implantation. Tumour progression was analysed in the kidney and surrounding serosa, and metastatic tumour presence in the lung, liver, spleen and bladder determined. After this, 80 rabbits were implanted with VX-2 in the lower pole and randomized into one of three groups: group 1, 35 rabbits treated 7 days after VX-2 implantation with cryoablation using a 15-min double-freeze technique and a 5-mm tumour margin target temperature of - 20 degrees C; group 2, 35 rabbits treated with open radical nephrectomy; or group 3, 10 untreated controls. Rabbits were maintained for 22 days and then killed; the kidneys, lungs, liver, spleen, urinary bladder and ureter were removed, and examined grossly and histologically for tumour presence. RESULTS: In the pilot study there was a consistent 50-100 mm(3) tumour after 7 days of growth, with no evidence of metastatic disease. By day 10 the mean kidney tumour was 230 mm(3) and two of three rabbits had metastases in the lung. By day 18 the mean primary tumour was 5504 mm(3) and all rabbits had metastatic disease. In the comparison study, cryotherapy cured 66% of implanted rabbits while nephrectomy cured 64%. All untreated controls had significant local and metastatic tumours. Findings in animals killed at 15 days after treatment showed significant differences between both treatment groups and untreated controls (P < 0.002). There was no difference in disease-free survival between the cryotherapy and open nephrectomy groups (P = 0.78) CONCLUSION: Both cryoablation and radical nephrectomy were effective in treating implanted VX-2 renal tumours compared with untreated controls. There was no statistically significant difference between cryoablation and nephrectomy.