1. 1. It was demonstrated by means of degradation of the sterols with chromium trioxide and isolation of 3β-acetoxy-methyl-cholanic acid that cholesterol is transformed by Asterias rubens into Δ 7-cholestenol. Further it was shown that β-sitosterol is converted into Δ 7-stigmastenol. It is supposed that all the dietary Δ 5-sterols can be converted into the corresponding Δ 7-sterols. 2. 2. It is unlikely that Asterias is able to dealkylate C 28 and C 29 sterols. After different pretreatments of the animals any trace of dealkylation activity could be detected. 3. 3. It was shown that sterols are catabolized rapidly. The nature of the various products formed from them was investigated. 4. 4. A scheme representing the main pathways in the sterol metabolism of Asterias rubens is given.