Plasma, erythrocyte and home tap water samples were taken from life-long residents of two counties (Evans-rural and Chatham-urban) in the high cardiovascular disease (CVD) belt of southeastern Georgia and from Habersham County, a rural county of North Georgia which is outside of the CVD belt. One-half of the subjects from each cohort had a serious CVD problem and the remaining half were healthy controls. Water samples were analyzed for hardness, total dissolved solids, pH and selenium (Se) content. Blood samples were analyzed for Se (by neutron activation analysis) and glutathione peroxidase (GSHPx). Se levels in all water samples were less than 0.01 ppb. Water hardness and total dissolved solids levels were higher in the CVD belt counties. There were no significant differences (P greater than 0.05), but water hardness and total dissolved solid levels were inversely correlated (p greater than 0.01) with the activity of erythrocyte GSHPx, a selenium containing enzyme which detoxifies oxidized fats.