Abstract Based on recently obtained analytical information, calculations were made to ascertain the toxic effects of chick edema factor (CEF) preparations for the intact day-old chick, the developing chick embryo, and the monkey. Results indicate that CEF, principally polychlorodibenzo-p-dioxins, elicits toxic responses in these experimental animals. For the intact chick, approximately 9 μ g./chick of total dioxins containing 2–8 chlorine atoms/molecule are detectable. For the fertile chicken egg, less than 1.0 ng. is detectable. For the monkey, as little as 2.15 mg. ingested for 445 days, or less, elicits obvious adverse effects. It is postulated that ingestion of these types of compounds may be toxic for man.