The clinical, haematological and biochemical correlations of 224 consecutive unselected examples of monoclonal gammopathy have been studied. The paraprotein frequency detedted was IgG 62 percent, IgA 15.2 percent, IgM 10.3 percent, Bence Jones protein 8.9 percent and in 3.6 percent the paraproteins were not identified. In half the monoclonal gammopathy was associated with an immunocytoma (myeloma in 82 and lymphoma in 30). In three cases the associated clinical disease was amyloidosis. In 36 cases (16.1 percent) the associated clincial disease was a nonlymphoproliferative malignant tumour. Monoclonal gammopathy may be a significant marker of malignancy in such cases. In 73 cases (32.6 percent) the associated clinical conditions were unrelated to the gammopathy although only 55 of these cases were sufficiently investigated to warrant classification as examples of benign monoclonal gammopathy. There was a strong correlation between Bence Jones proteinuria and malignancy. Sixty-five patients demonstrated Bence Jones proteinuria and in 59 of these a malignancy was detected. The association was strong between hypercalcaemia and malignancy as this was present in all 27 of the cases who had hypercalcaemia. The relationship between Bence Jones proteinuria and hypercalcaemia was also strong and Bence Jones proteinuria was detected in 73 percent of the hypercalcaemic patients as opposed to 36.7 percent in the whole series. Hypercalcaemia and Bence Jones proteinuria, when found in a patient with monoclonal gammopathy have a grave clinical connotation.