The fhit (fragile histidine triad) gene on chromosome 3p14.2 is a candidate tumour-suppressor gene; its abnormal transcripts are detected in several human cancers. To define the role of the fhit gene in the development of endometrial cancer, we examined 39 endometrial carcinomas for the presence of fhit gene alterations. fhit transcripts were analyzed by RT-PCR and direct sequencing. Loss of fhit transcript was observed in 6/39 (15%) tumours. Aberrant fhit transcripts, with deletions and/or insertions, were observed in 7/39 (18%) tumours but not in any normal endometrium. Allelic losses at D3S1300 and D3S4103, both located within intron 5 of fhit, were detected in 6/25 (24%) and 5/22 (23%) informative cases respectively. Expression of fhit protein was detected by immunohistochemistry; fhit protein was strongly expressed in 8/8 proliferative phase and 5/5 secretory phase endometria, also in 5/5 atrophic endometria; and it was strongly expressed in 6/6 simple hyperplasias without atypia, 6/6 complex hyperplasias without atypia, and 11/11 complex hyperplasias with atypia. In contrast, loss or reduced expression of fhit protein was observed in 13/27 (48%) endometrial adenocarcinomas. The impaired expression of the fhit protein was significantly correlated with the histological grade of the tumours. The present data suggest that inactivation of the fhit gene is an important genetic event associated with the genesis of endometrial carcinoma, especially with tumours of higher histological grade, which are believed to emerge directly from an atrophic endometrium. Int.