1. The acid, neutral and ‘intermediate’ salts of calcium bilirubinate have been synthesized.
2. All are crystalline, and the intermediate salt which has 1½ molecules of bilirubin per calcium atom probably has a crystal structure containing molecules of both acid and neutral salts.
3. The acid or intermediate salts have been found in 14 out of 70 gallstones analysed recently by X-ray diffraction.