Abstract 1. 1. The haemolymph of adult Artemia is frequently coloured blue-green by a glycoprotein complex, artemocyanin I. 2. 2. Artemocyanin II (M r 1.2 × 10 6), a structurally modified form of artemocyanin I purified from Artemia homogenates, has a blue chromophore which has been identified as a bile pigment related to biliverdin. 3. 3. It is suggested that the bile pigment is derived from the turnover of haemoglobin and is bound to artemocyanin for transport and excretion.