In tumour and corresponding kidney tissue from the 10 patients with RCC, the distribution of tumour/kidney ratios for CXCR4 and CXCL12α gene expression, calculated by real time RT–PCR and corrected for that of RPS9 ((CXCR4/RPS9)tumour/(CXCR4/RPS9)normal kidney and (CXCL12α/RPS9)tumour/(CXCL12α/RPS9)normal kidney, respectively), is given for each patient in Table 1 and Figure 1. The gene discussed is CXCR4; the disease is renal cell carcinoma.