This study further defines the region of consistent deletion of chromosome 7 in uterine leiomyomas. We have examined 74 leiomyomas for allelic loss of markers spanning the 7q22 region defined by markers D7S518 and D7S471. Forty tumors with cytogenetically defined 7q deletions, twenty-nine tumors without cytogenetically visible 7q deletions, and five tumors with no cytogenetic information were examined for allelic loss of D7S518, D7S666, D7S515, D7S658, D7S496, D7S692, and D7S471. Loss of heterozygosity for one or more of these loci was observed in twenty-eight leiomyomas with cytogenetically defined 7q deletions and in three leiomyomas with a normal karyotype. Allelic loss of D7S666 was common and was observed in all twenty-three informative tumors with 7q deletions and in two tumors with normal karyotypes. This study indicates the presence of a tumor suppressor gene in close proximity to the D7S666 locus. Eight tumors followed an unusual pattern of allelic loss. These tumors showed retention of heterozygosity for at least one locus flanked by deleted loci. These results suggest the possibility that two discrete regions of deletion at 7q22 are involved in the development of a subset of leiomyomas.