Abstract 1. 1. Asterosaponins were isolated from the gonads, the pyloric caeca, the stomach and the bodywall of female specimens of the sea star Asterias rubens. 2. 2. Thin-layer chromatography showed that the saponins of each organ consisted of a mixture. 3. 3. For each of the saponins the sugar and sulphate content (in nmoles) was determined. The ratio of these contents, indicating the number of sugar units per saponin molecule, was calculated. 4. 4. Statistical analysis showed that the sugar content in the saponins of the pyloric caeca was significantly lower than those in the saponins of the stomach, the bodywall and the ovaries, which in their turn were not significantly different from each other. 5. 5. The number of haemolytic units per μg SO 4 2− and per μg carbohydrate was determined for the various saponins. Haemolytic activity was roughly correlated to their sugar content, but also other aspects of the saponin structure are responsible for their haemolytic activity. 6. 6. Sugar composition was determined for each of the saponin mixtures. Each had its own specific composition, but in all cases quinovose was the main sugar. 7. 7. Mechanisms which could explain the probably organ-specific composition of the saponin mixtures are discussed.