The inhibitory effects of naringenin, eriodictyol, and luteolin (10(-5) and 5 x 10(-5) M), previously isolated from Satureja obovata subsp. obovata var. valentina (Lamiaceae), on rat thoracic aorta were investigated. Flavonoids at the two concentrations assayed (10(-5) and 5 x 10(-5) M) showed different smooth muscle relaxant behaviour in the three phases involved in the noradrenaline (10(-6) M)-induced contractions. The three flavonoids showed an inhibitory effect of the phasic component in order of potency: luteolin > eriodictyol > naringenin. Luteolin and eriodictyol inhibited both tonic-I and tonic-II phases associated to the inhibition of PKC and calcium influx, respectively, whereas naringenin only inhibited the tonic-I phase associated to inhibition of PKC.