Cases of cobalt (7440484) cardiomyopathy in workers in the mineral assay industry were described. The first case involved a 27 year old man who had suffered a flu like illness and exhibited increased right and left sided pressures, global hypokinesis, four chamber enlargement, mitral regurgitation, and trace tricuspid regurgitation, but no coronary artery disease. Right heart biopsy revealed hypertrophic myocardial cells with bizarre nuclei surrounded by irregular fibrotic areas. The patient's pubic hair contained 1.5 micrograms cobalt/gram of hair, a striking increase over control measurements which failed to detect cobalt. The second case involved a 19 year old man who was brought to the emergency room following a 1 day illness. He was admitted with cardiac failure and placed on an intraaortic balloon pump for stabilization prior to heart transplant. The cardiac cobalt level was 1.09 micrograms/gram. The first patient began working for a mineral assay laboratory in April of 1987 where sample preparation was carried out consisting of drying, crushing, pulverizing, homogenizing and splitting dirt, ore, or core samples to a powder with a particle size being less than 74 microns in diameter. Suboptimal hood capture velocities existed for exhaust fans at several of the stations. Cleanup was poor. The second patient began work at a different site as a crusher in the sample preparation area on the evening shift in June of 1989. Although warned, the patient failed to use his respirator.