We examined the pharmacological effects of intracerebroventricularly 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 micrograms) was given. The approximate anorectic potency was HED greater than CAD divided by PUT greater than ETD greater than 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.