also Besides morphines broad effects on the body systems,its most prominent effect is on the nervous system. this study was performed in to detennine the addictive effects of morphine on the brain of male rats in 1999. ln this researeh ,30 N-MARI male rats were randomly selected and divided in three groups of tens. The test group was injected with an increasing dose regimen of mophine -saline solution for 5 days (5-25 mg/kg ,BID) subcutaneously. The same dose of normal saline was used for the control group simultaneously .No injection was done on the control group after the last injection ,the animals were deeply anaes the tized ,then the brains were removed carefully the Skull and put in 10% formaline Solution. After 48 ltrs, the brains were embeded in a 7% agar . Then 1 mm coronal Slices were prepared by inventor macrotome. Afterward , using cavalieri principles , the volume of cerebral cortex was calculated . The volumes of the cerebral cortex in the test group, control goup I and control group2 were 624 63, 613/76,599/64 mm3 respectively. the finding proved no significant effect of morphine on the volume of cerebral cortex in rats.