1. 1. Large quantities of saponin are present in the Asteroidea (starfish), with only trace amounts in the Ophiuroidea, Echinoidea and Crinoidea. 2. 2. The occurrence of large amounts of saponin coincides with the presence of free Δ 7-sterols. 3. 3. Saponins exert their toxic effects by interacting with cell membrane cholesterol, and do not interact with Δ 7-sterols to the same degree. 4. 4. A relationship exists between the taxonomic position of a starfish and the composition of its saponin aglycone fraction. 5. 5. The starfish Marthasterias glacialis can synthesize saponins both from [2- 14C] mevalonic acid and [4- 14C] cholesterol.