1. The principal bile salt, myxinol disulphate, of two hagfish species, Eptatretus stoutii and Myxine glutinosa, has been shown by chemical methods and by optical-rotatory and mass-spectral considerations to be probably the C-3,27-disulphate ester of 3beta,7alpha,16alpha,27-tetrahydroxy-5beta-cholestane. 2. Myxine liver sterols were about half ;free' and half esterified: cholesterol only was identified. 3. The chemical nature of myxinol is what might be expected for the bile alcohol of a very primitive vertebrate.