We studied chromosome 10q loss of heterozygosity and PTEN/MMAC1 gene inactivation in renal cell carcinoma (RCC). Fifty-four cases of RCCs were analysed by three 10q RFLP markers. Forty one of them were heterozygous for at least one of the markers, of which fourteen showed LOH (34%). Six tumors which showed 10q deletion for RFLP markers and six randomly selected tumors without RFLP LOH were included in an extended study of 10q by eight microsatellite markers. Eight of these cases showed LOH with two smallest deleted regions (SRO) at 10q23 delineated by markers D10S541 and D10S579 while the other distal SRO is between markers D10S587 and D10S212 at 10q25-26. The five tumors with LOH covering 10q23 were selected for mutation analysis of PTEN/MMAC1 gene. One tumor without LOH of 10q23 was selected as a control. Using direct sequencing of nine exons, we found three different base pair changes in three tumors with LOH. Nine RCC cell lines were analysed for PTEN/MMAC1 gene inactivation. One homozygous deletion was detected in the cell line UOK147. No expression of PTEN/MMAC1 gene was detect by RT-PCR in the cell line UOK 147.