Degradation of ethylenebisdithiocarbamate fungicides (EBDCs) is known to produce ethylenethiourea (ETU). This article reviews the literature available on the toxicology of EBDCs and ETU, the sources in plants and persistence of ETU, and its formation during heat treatment of plant products. Detoxification techniques developed are mentioned, and Maximum Residue Limits and the results of monitoring studies are given for several countries. Some aspects of the methods of analysis are discussed. Although EBDCs have in the past been regarded as relatively harmless, data on their subchronic and chronic toxicity indicate that these toxicological features should not be ignored. ETU has low acute toxicity but possesses carcinogenic, goiterogenic, teratogenic, and mutagenic activity in animal tests. The most prominent aspect of its toxicology is its action on the thyroid gland, which causes hyperplasia and a decrease in thyroid hormone levels. It is a potent teratogen in pregnant rats after either acute exposure or administration throughout organogenesis, inducing a wide spectrum of malformations to the progeny. The teratogenic potential is specific to rat, whereas administration to pregnant mouse, hamster, guinea pig, and cat causes limited or no teratogenicity, except at very high dose levels. The mutagenicity of ETU has not been clearly established, although some data exist that indicate that it indeed has mutagenic potential. ETU can react with nitrites to form N-nitroso-ETU, which is a mutagenic and teratogenic compound. Most of the ETU present in fresh agricultural products treated with EBDCs arises from the presence of ETU in formulations. Surface deposits of EBDCs on plants may be a secondary source. ETU may also be taken up by plants from the soil following the breakdown of EBDCs, but conflicting results have been obtained on this phenomenon. ETU on plant surfaces undergoes subsequent degradation. Although small amounts may persist up to 30 d after spraying, there is no indication that it accumulates in plants. Initial findings that ETU is formed during the heat processing of EBDC-treated foods are confirmed by the more recent literature. However, the variability of the results indicates a wide range of conversion due to processing. Boiling of spinach, pears, grapes, tomatoes, and wheat, treated with different EBDCs, resulted in 3-30% conversion to ETU. Apple juice, dried pomace, and applesauce contained more ETU than the EBDC-treated apples, from which these products were produced. This was also true for tomato juice and canned whole tomatoes. ETU may be produced in the smoke of tobacco containing high EBDC residues.(ABSTRACT TRUNCATED AT 400 WORDS)