16 epithelial ovarian carcinomas (12 serous, 2 mucinous and 2 endometrioid) and 2 benign ovarian adenomas were studied using recombinant DNA technology to compare loci on chromosome 17 in germ-line and tumour DNA. Four polymorphic probes mapping to 17p and one mapping to 17q were used. There was a high frequency of allele loss on 17q/(77%) and a slightly lower frequency on 17p (69%). These findings probably indicate loss of tumour suppressor genes which are of fundamental importance in the genesis or progression of epithelial ovarian carcinomas.