To investigate possible involvement of CFTR in spermatogenesis, we used a CFTRknockout (Cftrtm1Unc, also referred as S489X) mice.Since most homozygous S489X CF mice die at a young age or less frequentlyavailable, heterozygous mice were used for quantitative measurement.Morphological study showed that testis tissue size and weight were significantlylower in heterozygous S489X CF mice than that of wild-type control (Fig. 1A). The gene discussed is CFTR; the disease is cystic fibrosis.