The erythrocyte sedimentation rate (ESR), plasma fibrinogen, serum orosomucoid, serum alpha 1-antitrypsin and serum haptoglobin were measured in 267 apparently healthy elderly subjects (median age 79 years, range 60-93), and compared to the values in 58 healthy younger subjects (median age 27 years, range 18-50). The acute phase reactants displayed no sex differences, but were significantly higher in elderly than in younger persons (mean +/- SD): ESR 13 +/- 10 mm/h vs 4 +/- 3 mm/h (p less than 0.001); fibrinogen 4.35 +/- 0.95 g/l vs 3.33 +/- 0.54 g/l (p less than 0.001); orosomucoid 0.68 +/- 0.20 g/l vs 0.60 +/- 0.16 g/l (p less than 0.01); alpha 1-antitrypsin 2.16 +/- 0.38 g/l vs 1.84 +/- 0.43 g/l (p less than 0.001); haptoglobin 1.30 +/- 0.50 g/l vs 1.00 +/- 0.30 g/l (p less than 0.001). Correlations existed between the acute phase reactants, being highest between ESR and fibrinogen (r = 0.53, p less than 0.001).