The endotoxin levels in serum of 377 72-year-old individuals were quantitated. The study population was a representative sample of this age group and was participating in a general study of health and disease among the elderly in Göteborg, Sweden. The endotoxin levels in serum were quantified by the chromogenic Limulus amebocyte lysate assay and were correlated with the health status and laboratory findings for each individual. The mean endotoxin levels (+/- 1 standard deviation) in men and women, when excluding four outliers, were 6.6 +/- 3.8 and 6.9 +/- 3.8 pg/ml, respectively. All included, 21.5% of individuals had endotoxin levels equal to or above the sensitivity limit of 10 pg/ml. Strong positive correlations were found between endotoxin levels and plasma triglycerides (P > 0.995) and between endotoxin levels and serum protein (P > 0.9875). The endotoxin activity also correlated with mean corpuscular hemoglobin concentration (P < 0.005, negative correlation), body mass index (P > 0.9875), and decreased appetite (P > 0.9875). A high alcohol consumption was associated with increased endotoxin levels (P = 0.995). There are no previous studies which examine endotoxin levels in serum samples from individuals representative of the population. This study showed that elderly individuals had the same mean level of endotoxin as has been found in other age groups. The increased endotoxin levels seen in heavy drinkers may be explained by a decreased ability of the liver to remove endotoxin. The correlations found between endotoxin and triglycerides, protein, mean corpuscular hemoglobin concentration, decreased appetite, and body mass index are discussed.