The circulating immune complexes were quantitatively determined by PEG-precipitation in the serum samples of 413 from the clinical point of view healthy persons subdivided into several age groups. In comparison with the other age groups the age group of 0-15 years showed the lowest immune complex values (mean = 3.14 +/- 0.96 mg protein/ml) with a significant higher distribution (p = 5%). Significant differences between the persons of the age of 16-30, 31-45 and 46-60 years were not traceable. The average values of the circulating immune complexes amounted to 3.82 +/- 0.75, 3.9 +/- 0.67 respectively 3.91 +/- 0.38 mg protein/ml. In comparison with these three age groups the circulating immune complexes showed with an average value of 3.62 +/- 0.75 mg protein/ml a falling tendency for the persons more than 60 years old. There existed a statistical significant difference (p = 5%) for the persons of the age of 31-45 years. A sexual dependence of the immune complexes could not be found within the age groups. Autoantibodies (ANF, anti-dsDNA antibodies) were traceable in the serum of 23 (24.7%) of the persons more than 60 years old. The comparison of the sera with and without autoantibodies didn't show any significant difference with regard to the immune complexes.