In March, 2022, a Working Group of 31 scientists from 13 countries met remotely at the invitation of the International Agency for Research on Cancer (IARC) to finalise their evaluation of the carcinogenicity of nine agents: cobalt metal (without tungsten carbide or other metal alloys), soluble cobalt(II) salts, cobalt(II) oxide, cobalt(II,III) oxide, cobalt(II) sulfide, other cobalt(II) compounds, trivalent antimony, pentavalent antimony, and weapons-grade tungsten (with nickel and cobalt) alloy. In two Good Laboratory Practice (GLP) studies2 in mice and rats, inhaled cobalt metal caused bronchioloalveolar carcinoma in male and female mice; bronchioloalveolar carcinoma, and malignant pheochromocytoma of the adrenal medulla in male and female rats; pancreatic islet carcinoma in male rats; and leukaemia in female rats. In two GLP studies in mice and rats, inhaled cobalt(II) sulfate caused bronchioloalveolar carcinoma in male and female mice; bronchioloalveolar tumours in male rats; and bronchioloalveolar carcinoma, and adrenal medulla tumours in female rats. In two GLP studies6 in rodents, inhalation exposure caused bronchioloalveolar carcinoma in male and female mice; fibrous histiocytoma and fibrosarcoma of the skin in male mice; lymphoma in female mice; and lung and adrenal medulla tumours in female rats.