Lack of Health Effects of Long-term Exposure to 2,3,7,8-Tetrachlorodibenzo-p-Dioxin

To the Editor.—  Regarding the potential health hazard of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in industrial wastes, an epidemiologic comparison between exposed and non-exposed groups from Quail Run, Mo, recently published in The Journal,¹ identified no consistent differences in medical history, physical examination findings, serum and urinary chemistry study results, and neurological test results. The subclinical differences in liver function test results reported are of dubious significance. However, since the authors suggested that long-term exposure to TCDD may be associated with depressed cell-mediated immunity, we wish to focus our comments on the immunologic data.A major point made is that the exposed group had a higher frequency of anergy and relative anergy than the control group. Skin tests for delayed-type hypersensitivity are notoriously subject to reader bias, especially in the hands of inexperienced readers, such as those used in this study. Observations made by two of the four readers were