Background. Total serum sialic acid is a recently investigated marker for cardiovascular mortality and carotid atherosclerosis. This study tested the hypothesis that past infection by Herpes simplex type 1 or type 2 viruses or Cytomegalovirus or Chlamydia pneumoniae accounts for the association between serum total sialic acid and atherosclerosis. Methods. Population-based samples of men and women living in four US communities were used in a cross-sectional study. Cases and matched controls were defined by B-mode ultrasound measurements of carotid and popliteal arterial wall thickness. In all, there were 267 case control pairs with information about antibody titres to viruses and 256 pairs with information about antibody titres to Chlamydia pneumoniae. Results. Serum total sialic acid (S-TSA) level was significantly higher in cases with carotid atherosclerosis compared to their controls. The odds ratio for carotid atherosclerosis associated with sialic acid level above 75th percentile was 1.73 (95% confidence interval [CI]: 1.02-2.95) in the sample with information about antibodies to viruses and 1.70 (95% CI: 1.00-2.93) in the sample with information about antibodies to C. pneumoniae. Adjustment for titres of antibodies to viruses and C. pneumoniae had no impact on the relation between sialic acid and carotid atherosclerosis. Conclusions. From these results, it seems unlikely that previous infection by any of these micro-organisms accounts for the relation between S-TSA level and carotid atherosclerosis.