Metallic coatings used for surface finishing or corrosion protection of instruments from the early twentieth century are shown to be a potential source of hazardous corrosion products. Several cadmium-coated metallic artefacts in the collections of the Museum of Natural History, Los Angeles County, were found to be actively deteriorating in storage. Analytical studies showed that these scientific instruments contained brass or iron components plated with cadmium and that corrosion of these coatings had resulted in the formation of a number of cadmium salts, probably including cadmium sulphide, CdS. Evidence for the presence of cadmium formate dihydrate, Cd(HCOO)2 2H20, was found by Fourier transform infrared (FTIR) spectroscopy on a set of headphones probably dating from c. 1925, showing that both organic acids and sulphur compounds in the storage environment have created active deterioration of these instruments. The highly toxic nature of these cadmium compounds poses a health risk in the handling of these objects during conservation treatment or curatorial examination. The instruments must be stored in an environment free from organic acid and sulphurous contaminants. Health and safety data for cadmium exposure are briefly reviewed.