In the August Nature Genetics , two groups report on their ongoing large-scale projects to produce mouse mutants using the chemical mutagen ethylnitrosourea. An English and French group have screened over 26,000 F1 progeny for dominant defects in growth and development, and a subset of these for defects in neural and behavioral function and blood chemistry (Nolan et al ., Nat. Genet . 2000, 25 :440-443). Their results are cataloged in Mutabase . Approximately half of the phenotypes are heritable, and an extrapolation from present numbers suggests a final count of about 500 mutants. These mutants (with phenotypes in parentheses) include such memorable additions as spin cycle (head bobbing, fits), nanomouse (small and pointed head), and van gogh (craniofacial, lowered ear).