We examined sections of fallopian tube from 99 patients with serous borderline tumors of the ovary (SBT) to determine the prevalence of epithelial hyperplasia. Fifty-eight patients with carcinoma of the cervix (CC) and 30 with grade 2 or 3 ovarian carcinoma (OC) served as controls. Patient ages were similar in each group. Epithelial hyperplasia was identified in 68 of 99 patients with SBT (68.7%), compared with 15 of 58 with CC (25.9%) and 4 of 30 with OC (13.3%). Epithelial thickness and nuclear crowding were greater in hyperplas-tic than in normal fallopian tubes. There was no correlation between hyperplasia and menstrual cycle. In patients with SBT, the presence of epithelial hyperplasia correlated with tumor stage. Hyperplasia was present in 38 of 60 (63%) patients with Stage I tumors. In Stage II and III tumors, hyperplasia was present in 18 of 25 (72%) patients with noninvasive peritoneal implants and 12 of 14 (86%) with invasive implants. Fallopian tube epithelial hyperplasia may represent an example of a field effect in müllerian carcinogenesis.