HETEROCYCLIC SULFIDE

PURPOSE: To obtain a medicine for immune stimulation, immune resurrection and cytostatic treatment, comprising a specific heterocyclic sulfide. CONSTITUTION: This medicine comprises a compound of formula I [Het is a five-membered or six-membered heterocyclic ring which may be substituted; R is an alkyl, an alkenyl or a cycloalkyl in which O, S or an NR' (R' is a 1-4C alkyl) can be present in the chain or which may be substituted or a cycloalkyl which may be optionally substituted], with the proviso that a compound of formula II ((n) is 1-5) is omitted, such as 2 methylmercapto-4-methyl-1,3- thiazol-5-ylacetic acid as an active ingredient. The compound has an LD50 value larger than 1,000mg/kg in intravenous injection of mouse, 0.5-100mg/weight Kg and cytostatic amount effective for warm-blooded mammal by parenteral and oral administration and shows no toxicity in the administration.