Erratum.
In the letter "Kepone chronology" by Rudolph J. Jaeger (9 July, p. 94, column 3, paragraph 3, line 9), the airborne Kepone concentration in the Life Science Products plant measured by state of Virginia officials in July 1975 was erroneously given as 3 mg/cm(3). The correct concentration was 3 mg/m(3). A portion of a sentence in the preceding paragraph was also erroneously omitted (line 14). The sentence should have read, "A chronicity factor, calculated from these data, is the ratio of the single LD(50) value divided by the LD(50) value in repeatedly dosed animals."