CA125/MUC16 mucin is a high-molecular-weight glycoprotein overexpressed in the majority of serous carcinomas, the most common histological type of ovarian cancer, but is not detectable in the epithelium of normal ovaries (Kabawat et al, 1983; Davis et al, 1986; Nagata et al, 1991; De los Frailes et al, 1993; Kobayashi et al, 1993). Here, MUC5AC is linked to serous adenocarcinoma.