This paper presents a new dual color FISH technique that will allow the use of cell specimens isolated from formaldehyde-fixed and paraffin-embedded (F-P) tissues. The new FISH method was used to examine numerical aberration in chromosome 17 and c-erbB2 gene amplification in 26 F-P epithelial ovarian cancer tissues. Numerical aberration of chromosome 17 appears frequently in clear cell adenocarcinoma. The frequency of amplification of the c-erbB2 gene in stage III and IV cases was significantly higher than in stage I cases. The FISH technique as established here may serve as a molecular tool for examination of clinico-pathological significance in F-P tissues.