Loss-of-function mutations in CFTR are associated with absence of the vas deferens and epididymis abnormalities in cystic fibrosis (CF) (Landing et al, 1969; Holsclaw et al, 1971) and abundant CFTR expression is seen in the genital duct epithelium of humans and many other species (Harris & Coleman, 1989; Harris et al, 1991; Pollard et al, 1991; Bertog et al, 2000; Leung et al, 2001). The gene discussed is CFTR; the disease is cystic fibrosis.