Abstract-We examined the pharmacological effects of intracerebroven tricularly administered aliphatic diamines on ingestive behavior in male rats adapted to a 4 hr per day feeding and drinking schedule. 1,2 Ethanediamine (ETD), 1,3-propanediamine (PRD), 1,4-butanediamine (putrescine, PUT), 1,5-pentanediamine (cadaverine, CAD) and 1,6 hexanediamine (HED) suppressed feeding and drinking behavior in a dose dependent manner, but not unless a relatively high dose (over 80 /1g) was given. The approximate anorectic potency was HED>CAD=PUT> ETD>PRD. A sedation was also produced in fairly good parallel to these alterations in feeding and drinking behavior. Thus, there appears to be a relationship between the length of the carbon chain and the potency of the pharmacological action, and these inhibitory effects on feeding and drinking behavior are probably not due to a specific action on the regulatory system for ingestive behavior, but rather to a nonspecific action.