Total and ionized calcium and other related parameters were measured in 34 patients with multiple myeloma. Hypercalcemia was not a major feature of the group of patients studied with only three patients exhibiting marked increases in total (Ca total) and ionized (Ca++) calcium concentrations. The Ca++/Ca total ratio was also maintained within relatively narrow limits. No major differences were found in the calcium fractions of patients with different types of multiple myeloma. Serum immunoreactive parathyroid hormone showed no consistent relationship with either the total or ionized calcium concentration. There were no correlations between increased total protein or reduced serum albumin concentrations and changes in total and ionized calcium fractions or Ca++/Ca total ratios. These results imply that in this group of myeloma patients, there was no significant binding of calcium by the monoclonal immunoglobulins.