The purpose of this study was to determine the usefulness of color vision screening in identifying patients with elevated digoxin levels ( 2.0 ng/ml). Test-retest color vision measurements were obtained on 56 subjects with elevated digoxin levels and 93 nondigoxin subjects. Two tests, the Ishihara and Sahlgren's Saturation Test (SST), identified digoxin levels of 2.9 ng/ml or more. These tests also yielded a high percentage of improved retest scores among subjects with elevated digoxin levels ( 2.7 ng/ml) of more than 4-days duration and a low percentage of improved retest scores among the nondigoxin group. The Ishihara, SST, and other bedside color vision tests may prove useful in the routine monitoring of patients on digoxin therapy, especially those with a high risk for toxicity.