In mammals, as well as teleosts, DAX-1 (Dosage-sensitive sex reversal, adrenal hypoplasia congenital, critical region on the X-chromosome, gene-1), FOXL2 (forkhead box L2), cytochrome P450 aromatase, MIS (Mullerian inhibiting substance), SF-1 (steroidogenic factor-1), SOX-9 (SRY-related, high-mobility group (HMG) box (SRY box)-9), WT-1 (Wilm's tumour-1) [3-6] and many other gene products contribute in directing sex-determined fates, as well as to subsequent gonad development and function [7-9 and refs. therein]. The gene discussed is FOXL2; the disease is chronic primary adrenal insufficiency.