For two years protein abnormality was studied in 40 cases of myelomatosis in Jamaica. Thirty-nine of these were in West Indian Negroes. The minimum incidence of myelomatosis in this group was estimated to be of the order of 50 cases per million per annum which is considerably higher than in Caucasians as reported by previous workers. A larger number showed myeloma protein with beta-globulin mobility and hypogammaglobulinaemia than with gamma-globulin mobility. As in the Caucasians the disease is more common in men than in women and the age incidence in both seems to be the same. Combined serum and urinary electrophoresis was diagnostic in every case, and examination of the urine for Bence-Jones protein by electrophoresis yielded more consistent findings than the classical heat test. It is suggested that combined serum and urine electrophoresis should be done in all cases of suspected myelomatosis.