Deletions within the short arm of the human chromosome 11 have been found to be involved in the genesis of several tumours, including different urogenital neoplasms. We have studied 31 male germ cell tumours (19 seminomas and 12 nonseminomas), and observed loss of heterozygosity at 11p loci in 40% (12/30) of these tumours [35% (9/26) at 11p13 and 31% (8/26) at 11p15]. Our data suggest that inactivation of one or more tumour suppressor genes on 11p are involved in the genesis of testicular cancer. In addition, identification of the parental origin of the allelic losses revealed a paternal loss in six patients and a maternal loss in one case.