Urol--a compound of extracts from rad. Rubiae, sem. Ammeos visnagae, herb. Virgaureae, rad. Taraxaci and aescin - induced changes in the mechanical activity (isotonic registration) of guinea pig and rat ureter, detrusor and vas deferens preparations when applied at concentrations of 10 ng to 100 microgram/ml. Low concentrations (10 ng to 1 microgram/ml) had an inhibitory effect on the spontaneous mechanical phasic activity in about half of the ureter preparations and a stimulatory effect on the remaining preparations; higher concentrations (1-100 microgram/ml) had a predominantly inhibitory effect. Urol acted similarly on detrusor preparations; it inhibited (up to 30% at 10 mg/ml) or stimulated the contractile responses after nerve stimulation (10 Hz, 0.3 ms, 3 s); it had a purely inhibitory effect on the contractions of vas deferens after nerve stimulation and had an inhibitory effect on X-ray-induced contractions in detrusor muscle preparations. The effects of Urol were observed at therapeutically relevant concentrations (about 1-10 microgram/ml). The nonuniform effects of Urol on urinary tract preparations suggest a reason for the differences in therapeutic response observed in clinical trials.