Immunohistochemical expression of EGF-R, c-erbB-2 and c-erbB-3, members of the type-1 family of receptor tyrosine kinases, were investigated in 67 primary ovarian-tumour samples (46 malignant, 8 borderline and 13 benign), and related to tumour clinicopathological features. The incidence of all 3 receptor proteins was highest in overtly malignant tumours. No significant correlations were observed between either EGF-R or c-erbB-3 and clinical parameters such as tumour stage, differentiation or extent of debulking surgery, but c-erbB-2 was significantly associated with several indicators of prognosis, including early stage and good/moderate differentiation in optimally debulked tumours. Multiple expression of c-erbB receptor proteins was also significantly higher in malignant tumours compared with borderline and benign tumours. Early-stage tumours were also more likely to express multiple c-erbB-receptor proteins than were late-stage tumours. Co-expression of EGF-R with c-erbB-2, and c-erbB-2 with c-erbB-3 was significantly greater in malignant tumours than in borderline or benign tumours, and within the malignant tumour group, positive associations were observed between EGF-R and c-erbB-3, also between c-erbB-2 and c-erbB-3. Because of the evidence of increased expression of individual c-erbB proteins as well as multiple expression of this family of growth-factor receptors in malignant ovarian tumours, we hypothesize that stimulation by the appropriate ligands may confer a selective advantage to cells expressing more than one receptor. Increased expression of c-erbB growth-factor receptors in malignancy may mediate increased propensity for tumour development.