Isoxazolecarboxamide derivatives (I) (R=alkyl, alkoxy, polyfluoroalkoxy, OH or CF3SO2O; each of R1 and R2 independently =H, halogen, polyfluoroalkoxy or alkoxy; R3 = one or more substituents selected from H, halogen, alkyl, alkoxy, NO2, NH2, NHacyl, CN, alkoxycarbonyl, carboxamido; R4 = H, alkyl or aralkyl; an n is 0, 1 or 2) and their N-oxides and pharmaceutically acceptable salts are endowed with adrenergic antagonist activity and high selectivity toward the αla adrenergic receptor with respect to the 5-HTlA receptor. This activity profile suggests the use of these derivatives in the treatment of obstructive syndromes of the lower urinary tract, including BPH, without side effects associated with hypotensive activity being present.