[en] Radioprotective agents are first defined, and then a brief bibliography of relevant books, reviews and general discussions follows. The chemical names and formulae of radioprotective agents are listed with their accepted abbreviations and corresponding patented names. An historical introduction identifies four main steps in the development of knowledge of chemical protection against ionizing radiations. Possible mechanisms of the radioprotective behaviour of different compounds are discussed. A table of sulphur-containing compounds with dose (mg/kg) and any radioprotective effect in various mammals identifies a common structural feature of the most active protective agents as a two or three carbon chain with a strong basic group (amino or guanidino) at one end and a thiol at the other. These compounds have chelating properties. The significance of the intramolecular transguanylation of AET to MEG (mercaptoethylguanidine) in phosphate buffer is emphasised. It is suggested that the sulphur-containing radioprotective substances should be considered as a particular class of drugs, since they exhibit peculiar, rapid transient toxic effects in mammals at the dose required for radioprotective action. (U.K.)