Epidemiologic studies on chromate workers are considered with special reference to the valency of chromium compounds, carcinogenic potency, and water solubility. It is assumed that all hexavalent chromium compounds are carcinogenic to humans when inhaled but that there is no evidence that trivalent compounds are carcinogenic. It is suggested that zinc chromate is a highly potent carcinogen and also that calcium chromate may be carcinogenic. There are indications that chromates of low water solubility may be less potent carcinogens than compounds of greater solubility. Evidence is also presented for possible interactions with smoking and other factors involved in work-related cancers.