1. 1. Animals belonging to the five classes of echinoderm have been shown to contain high concentrations of steryl sulphate. 2. 2. The steryl sulphates of a crinoid and an ophiuroid contained a higher proportion of cholest-5-en-3β-ol than was present in the free Δ 5-sterol mixture. 3. 3. The two echinoids examined contained less steryl sulphate than was found in the other echinoderms and the proportion of C 27 Δ 5-sterol was about the same in the free and the sulphated forms. 4. 4. All the asteroids and the holothuroid examined contained free C 26, C 27, C 28 and C 29 Δ 7-sterols but the steryl sulphate was dominated by cholest-5-en-3β-ol and 5α-cholestan-3β-ol. 5. 5. The ophiuroid, Ophiocomina nigra, was shown to convert injected radioactive cholest-5-en-3β-ol into its sulphate. 6. 6. The crab Carcinus maenas contained traces of steryl sulphate but steryl sulphates were not detected in Chlamys opercularis, Buccinum undatum (Mollusca), Hymeniacidon perleve (Porifera), Metridium senile (Coelenterata), Arenicola marina (Annelida) or Ciona intestinalis (Chordata).