A method, based on the Delphi technique, for evaluating occupational risks in a quantifiable manner was devised in the course of a case-control study on respiratory cancers in the nickel mining and refining industry in New Caledonia. There were four stages in the evaluation process: identification of eleven potential carcinogenic factors in the company during the 1930-1977 period; grouping of a limited number of work-stations; evaluation of exposure levels for the different factors for each workstation; computation of the cumulative value of exposure for each subject under study. A partial validation study shows that this kind of approach may prove useful for future occupational epidemiological studies.