To learn more about the effects of ambient air pollution on the human immune system, immunological parameters-16 serum proteins and circulating immune complexes--were determined for more than 500 women from the polluted area of Cologne, Germany, and a control area, Borken. The geometric mean values for immunoglobulins, complement components, haptoglobin, alpha 1-acid glycoprotein, alpha 1-antitrypsin, ceruloplasmin, alpha 2-macroglobulin, prealbumin, and transferrin were statistically significantly higher in Cologne than in Borken. No difference were found for C-reactive protein, rheumatoid factors, and anti-streptolysin O. For each of the parameters a logistic regression was fitted, thus controlling for the influence of a number of confounding factors. After controlling for possible confounders, the percentages of values above the norm for immunoglobulins, complement components, haptoglobin, and alpha-1-glycoprotein were statistically significantly higher in Cologne than in Broken. Important confounders included overweight, high blood pressure, acute cold, fever in the preceding week, and smoking. The biochemical mechanisms underlying the observed interarea differences in protein profiles are as yet unknown and should be the subject of further, nonepidemiological research.