Laboratory-test results for a population of immigrants living in north-east France revealed differences between the concentration of the blood constituents of immigrants and native French people. By immigrants we mean persons now living in France but coming from other geographical locations such as Italy, the Iberian Peninsula, northern or central Europe, northern Africa, or the Near or Middle East. Multiple regression analysis confirmed the need to establish reference limits in immigrants for many blood constituents because of a significant shift of the curve relative to that for the French population. We have determined appropriate reference limits, for some ten blood constituents in each group of immigrants.