Dissociation constants involving Ca (super ++) , Mg (super ++) , Na (super +) , K (super +) , SO 4 (super --) , HCO 3 (super -) , and CO 3 (super --) ions, and individual ion activity coefficients have been used to calculate the distribution of dissolved species in sea water at 25 degrees C. and one atmosphere total pressure. The distribution obtained for sea water of chlorinity 19 o /oo and pH 8.1 are given. The activities calculated for free ions are also given.