The condition index of bivalves is measured by relating either the weight or volume of the meat to some aspect of the shell. Separation of the meat and shell by dissection in small spat is impracticable and this paper examines the value of an ashing technique to obtain a ratio of ash weight to organic matter weight. The results were consistent and the calculated condition index was closely related to an index obtained by dissection. Ashing dissected spat showed that 35 to 59% of the organic matter is in the shell.