The serum level of immunoglobulin E (IgE) was found to be significantly greater than normal in a group of 23 out of 28 patients with atopic dermatitis. Each member of this group also showed several positive reactions to intradermal tests with 36 common antigens. The three atopic patients with the lowest IgE levels gave negative or, in one case, a single weak intradermal test. There was no correlation between the IgE level and the severity of clinical symptoms or a history of asthma or hay fever. IgE values were generally normal in a group of 34 patients with acute or chronic urticaria and in a larger group of patients with nonatopic dermatitis and various dermatological conditions.