Global Ret deficiency results in neonatal lethality because of renal agenesis (Schuchardt et al., 1994; Durbec et al., 1996), and because Pax2Cre is expressed in intermediate mesoderm, Pax2Cre/Ret mutants in our colony also died in the early postnatal period. This evidence concerns the gene RET and renal agenesis.