The use of anabolic agents may give rise to residues in foods of animal origin and thus to potential effects on public health. Therefore, the physiology, metabolism and toxicity of the three endogenous hormones. 17 beta-oestradiol, progesterone and testosterone are discussed. In addition, the effects of the use of three exogenous hormones, diethylstilboestrol (DES), trenbolone and zeranol are evaluated. As can be expected all six compounds have effects on the endocrine system and reproduction. Endogenous hormones and DES are teratogenic at high-dose levels. With the exception of DES, there is no evidence of a mutagenic action. 17 beta-Oestradiol and testosterone were shown to induce tumours at high-dose levels in experimental animals; probably however, a threshold can be established. The residues in edible tissue resulting from the use of endogenous hormones are much smaller than are the natural levels in cow's milk and butter. In view of the carcinogenicity of DES in man, its use should be strongly discouraged. A definite statement on the acceptability of the use of trenbolone and zeranol cannot be made.