Abstract The development of new anthelmintics for use in livestock has been probably the most rapidly expanding area in the field of pharmaceutical research of recent years. Scarcely a month goes by without the reporting of yet another new compound being introduced for its novel anthel-mintic activity. The real revolution in nematode therapy began in essence with the discovery of Thiaben-dazole in the early 1960s. This success stimulated considerable research activity and heralded the onset of the modern era of anthelmintic compounds. Since that time great strides have been made in the discovery of nematocides, fasciolicides and cestocides, all possessing increasing potency and broad-spectrum activity. Modern research has provided us with a considerable array of highly effective and highly selective drugs with which to attack helminth parasites. It is of paramount importance that these agents be used correctly and judiciously if a favourable clinical response to treatment is to be obtained.