Forty-six plate painters, heavily exposed to cobalt blue dye, took part in this cross-sectional study, and 51 top-glaze painters served as the referents. The study comprised a questionnaire, a health examination, a lung function test, and the determination of the blood and urinary cobalt levels. The plate painters were examined twice, at the end of a workfree period and after resuming work. More plate painters complained of irritation from the mucous membranes in the mouth and throat, cough, and expectoration than the referents. The symptoms increased after the plate painters resumed work. The cobalt level of the plate-painting group after six weeks off work was twice as high in the blood and five times higher in the urine than the corresponding values of the reference group. After the plate painters resumed work, the blood and urinary levels increased approximately 4 and 15 times, respectively. Increased airflow resistance was found in the plate group when compared with the referents, and signs of small airway obstruction increased after the plate painters resumed work. The pulse rate was higher among the plate painters, and minor changes in the red blood cell picture were observed. None of these adverse health effects were associated with the cobalt levels in the blood or urine.