Technical Abstract: Background: Supplemental Se may reduce cancer risk in individuals below a threshold Se status, e.g., a plasma Se concentration of ca.106 ng/ml. A more informative means of characterizing Se status in non-deficient individuals is needed. Objective: Elucidate the relationships among biomarkers of Se status and relevant metabolic and genetic factors in non-deficient individuals. Design: In a cohort of healthy men (n=106) and women (n=155), several biomarkers of Se status (plasma Se, plasma selenoprotein P [SEPP1], plasma glutathione peroxidase activity [GPX3], buccal cell Se, urinary Se) were evaluated in relation to selenoprotein genotypes (GPCX1, GPX3, SEPP1, selenoprotein 15), dietary Se intake, and parameters of single-carbon metabolism. Results: Plasma Se concentration was 142.0±23.5 ng/ml and estimated Se intake was 114.4±47.9 µg/d. Plasma GPX3 and SEPP1 comprised 10% and 34%, respectively, of plasma Se, with 47% present as non-specific components accounting for virtually all of the interindividual variation. Buccal cell Se was associated with age and plasma homocysteine (hCys), but not plasma Se. SEPP1 showed a quadratic relationship with body mass index, peaking at BMI 25-30. Urinary Se was greater in women than men, and was associated with metabolic body weight (kg0.75), plasmas folate, vitamin B12 and hCys (negatively). A GPX1 genotype (679T/T) had lower plasma Se than other allelic variants. Fasting plasma glucose and HbA1C were not associated with plasma Se. Conclusions: Genotype, methyl-group status and BMI contributed to variation in Se biomarkers in this Se-adequate cohort. Individual differences in plasma Se concentration were largely due to differences in the non-specific component of plasma Se.