The effect of an Egyptian medicinal plant, Cleome droserifolia (Forssk.) Del. on nitric oxide (NO) produrtion in bacillus Calmette-Cuerin-induced moiise peritoneal macrophages arti-vated by lipopolysaccharide was investigated in vitro. The methanoi extract of C. droserifolia reduced the NO produrtion, and two flavonoids were isolated as the active components. The new one was determined to be 5,4′-dihydroxy-6,7,8,3 ′,5′-pentamethoxyflavone ( 1) and the other was identified as 5,4′-dihydroxy-6,7,8,3 ′-tetramethoxyflavone (8-methoxycirsilineol; 2). Compound 1 concentration-dependently suppressed the NO production and was effective at a non-toxic concentration (12.5 μ/ml). The suppressive activity of 2 was weaker than that of 1.