AbstractThe possible bronchocarcinogenic effects of fumes released during the shielded metal arc welding of stainless steel and the thermal spraying of chromium oxide (Cr2O3) have been studied on the rat. The fume particles were shown to contain tri‐ and hexavalent chromium in soluble and low soluble forms; they were collected and implanted as pellets in the bronchi of groups of 100 rats by the method of Laskin et al. A negative control group of 100 rats was included, as well as positive controls receiving pellets containing benz(a)pyrene. The experiment was continued for 34 months; no differences of biological significance were noted between the growth rates, survival times, and terminal organ weights of the test and negative control groups. At autopsy, the macroscopic and microscopic appearance of the organs in the three groups, including the local reaction to the implanted pellet, were similar. No precancerous changes were observed at the implantation sites; one rat, who received a pellet containing welding fumes, showed squamous cell carcinoma remote from the implantation site and not associated with the bronchus. It had the appearance of a metastasis. All three benz(a)pyrene control rats developed cancer at the implantation site. The occupational health implications of these findings are discusse