The anti-oxidant phenotype was determined in red blood cell haemolysates of 62 healthy elderly persons (Mean age: 56) and a number of male silicosis patients (Mean age: 65, n = 19). Moreover, analysis of water-soluble fluorescent substances in plasma, recently introduced as a new test for in vivo lipid-peroxidation, was included. Within the control group results were analyzed on the effect of smoking (no effect), use of medication (lowered GSH-content) or gender (no differences apart from haemoglobin content). No simple relationship between any pair of the measured parameters in erythrocytes was present. When comparing the male control persons with the silicosis group a significantly higher red blood cell GSH-level was observed in the latter. Moreover, some factors of the anti-oxidant system are strongly correlated in the diseased, but not in the healthy subjects.