We thank Rylander for his interest in our article and for suggesting magnesium may confound the association we observed between inorganic arsenic in water and risk of coronary heart disease. We did not include measures of drinking water magnesium (or hardness) in our study. However, levels of calcium and magnesium reported for the Rio Grande aquifer (which served our study population in the San Luis Valley) indicate higher levels of hardness, with low variability in the San Luis Valley ( Robson and Banta 1995 ). In contrast, the arsenic level in groundwater in the San Luis Valley water quality samples showed considerable variability of 0–95 µg/L.