The accidental finding of intense fluorescence of the toenails and fingernails of persons receiving quinacrine hydrochloride (atabrine) was first noted in December 1945. This occurred when one of us (R. R. K.) was examining a patient with the Wood light and noticed a brilliant yellow-green fluorescence of the examiner's nails, as shown in the accompanying illustration. This examiner had just returned from the Southwest Pacific Theater, where he had been taking atabrine in daily doses for almost two years. The fluorescence of the so-called normal nail is much less intense than that of the "atabrine" nail and its color is quite different, in the normal nail being violet-blue and in the "atabrine" nail being yellow-green to almost white. Since then an additional 9 persons have shown this fluorescence. All of them had taken atabrine from five to twenty-one months. In no person not receiving atabrine has this fluorescence been observed.