We report experience measuring serum ionized calcium (Ca2+) with new solid-state, specific calcium ion dip electrodes in a commercially available system for automated electrode measurments which permits stable measurements on thirty samples with up to six different electrodes simultaneously. The system provides electrostatic shielding, temperature regulation at 37degreeC, and adjustment of serum pH with CO2 gas, thereby making practical the use of serum standards and routine measurements on sera. When the electrodes are used with the rest of the measuring system and with serum standards, the system provides serum Ca2+ measurements with high precision (C.V. of 0.7%) and the calcium electrodes maintain good slopes for 50 to 150 hours of cumulative wet immersion. Response to new calcium activity is rapid, and wide variations in serum Ca2+ are readily measured.