Living organisms are known to respond to various types ofenvironmental stress factors. The response is observed whenthe magnitude of stress exceeds a minimum amount calledthreshold. However during the past few decades, response ofthe living organisms below the threshold came to the purviewof the scientists. Some stress factors are found to elicit abiphasic response viz, stimulation at low dose and inhibitionat high dose. The phenomenon called hormesis plays a crucialrole in the acclimatization of organisms to the environment.Physical and chemical factors that elicit hormetic type responsesare called hormetins. The importance of some chemicalsthat mimic the effect of hormetins in therapeutics is beginningto be understood.