Previous reports have shown that one copy of the chromosome 17 was frequently lost in human ovarian cancers (1). The position of the allelic deletion has not been mapped and involvement of p53 gene has not been determined. In this study, we have shown that in human ovarian carcinoma, the commonest region of allelic loss in chromosome 17p is 17p 13.3 (65%) and 17p13.1 (63.7%; 6 out of 9 informative cases). Allelic loss was also observed at region 17p12 - 11.1 but at a lower frequency (38.6% to 37.5%). The pattern of allelic loss of p53 gene was consistent in both primary and secondary metastatic tumors of the same patient. No gross rearrangement of p53 was however observed at the remaining allele using Southern blot analysis. Allelic loss of p53 gene was closely associated with 17p 13.3, the terminal portion of chromosome 17p. The high frequency of allelic loss of p53 gene in ovarian carcinomas conformed with recent findings in cancers of colon, breast, lung and brain suggesting inactivation of p53 gene play a rate limiting step in pathogenesis of human malignancies.