Ferula harmonis, which is locally called 'zallouh' in the Middle East, is used as an aphrodisiac as it is reputed to enhance male sexual behavior, however, there is no scientific verification. In this study, the oil extracted from the seeds of Ferula harmonis was tested for its efficacy in enhancing erectile function and toxicity in male rats. The sexual activities assessed by penile erection index were dose dependent. The ED(50) (12.03 mg/kg) was 880 times less than the LD(50) (10.6 g/kg). However, when doses ranging from 0.05, 0.5 to 2 g/kg were given daily for 28 days, acute and subacute toxicity were observed. There was a decrease in total body weight, hepatomegaly, atrophic testis, significant decrease in hemoglobin and red blood cell count. In addition, there was a significant decrease in cholesterol level. All the above indicate that the crude oil from the plant Ferula harmonis can enhance erectile function, however, it becomes toxic if it is used for a long period of time. Further studies are underway to isolate and identify the active ingredients and their exact mechanisms of action.