This study investigated the frequency of allelic imbalance (AI) in particular loci in conventional renal cell carcinoma tissue and premalignant lesions of the kidney. DNA from the tumor tissue, premalignant lesions and normal kidney tissue of radical nephrectomy specimens from 33 patients was obtained. It was amplified with a set of eight microsatellite markers, which are located on chromosomes 2, 3, 5, 8, 9, 11, 16, 17. AI in DNA samples was determined by analysis of the alteration in (CA)n repeats. The rates of AI in tumor tissue were found to be between 22.2% and 53.3% and in premalignant lesions between 11.1% and 40.0%. Premalignant lesions and tumor tissues in conventional renal cell carcinoma have the same genotypic changes in 50.0-87.8% (informative cases). These results suggest that the progressive accumulation of AI in areas of premalignant lesions may contribute to the development of renal cell carcinoma, representing an important molecular event in the multistep renal carcinogenesis cascade.