1. The echinoderms Asterias rubens and Solaster papposus (Class Asteroidea) metabolize injected [4(-14)C]cholest-5-en-3beta-ol to produce labelled 5α-cholestan-3beta-ol and 5α-cholest-7-en-3β-ol. 2. Conversion of 5α-[4(-14)C]cholestan-3β-ol into 5α-cholest-7-en-3β-ol was demonstrated in A. Rubens. 3. Incubations of A. rubens with [4(-14)C]cholest-4-en-3-one resulted in the production of labelled 5α-cholestan-3-one, 5α-cholestan-3β-ol and 5α-cholest-7-en-3β-ol. 4. [4(-14)C]Sitosterol was metabolized by A. rubens to give 5α-stigmastan-3β-ol and 5α-stigmast-7-en-3β-ol. 5. The significance of these results in relation to the presence of α7 sterols in starfish is discussed.
