We examined 35 primary human ovarian adenocarcinomas for the presence of epidermal growth factor (EGF) receptor (EGFR) in plasma membranes from cancer tissues by using 125I-EGF as a ligand. Specific 125I-EGF bindings were observed in 20 (57%) of these 35 cases. Scatchard analysis showed a class of high affinity EGF receptor: Kd, 5.0 ± 1.0 × 10-10 m; Bmax, 83.3 ± 12.1 fmol/mg protein (mean ± SE, n = 20). Northern analysis in polyadenylated RNA from 15 EGFR(+) cancers using pretransforming growth factor α (pre-TGFα), prepro-EGF complementary DNA, and pE7, a complementary DNA clone of human EGFR, as probes revealed that pre-TGFα and EGFR mRNAs but not prepro-EGF mRNA were expressed in all cases examined. Immunocytochemical studies using monoclonal antibodies (mAbs) against TGFα, EGF, and EGFR showed that TGFα and EGFR but not EGF proteins were present on ovarian cancer cells in all cases. These data suggested a possible TGFα/EGFR autocrine mechanism in EGFR(+) ovarian cancers. We, therefore, examined the biological significance of this autocrine mechanism by using primary monolayer cell cultures. In primary cultures from EGFR (+) cancers, TGFα added to the culture medium stimulated the [3H]thylmidine incorporation dose dependently. Moreover, the addition of mAbs against TGFα and EGFR but not EGF inhibited [3H]thymidine incorporation dose dependently in EGFR(+) cancer cells. On the other hand, in primary cultures from EGFR(-) cancers, TGFα and anti-TGFα, -EGFR, and -EGF mAbs did not show any effects on [3H]thymidine incorporation. All these results suggested the possible crucial role of a TGFα/EGFR autocrine growth mechanism in primary human ovarian cancers which express EGFR.