<p>Oxazolidinones of general formula (I): R = alkenyl with minimum 2 and pref. max. 4C atoms Z = O or S. The new cpds. inhibit adrenergic beta-receptors and are also valuable intermediates in the prepn. of other pharmacologically active cpds. 3-Isopropyl 5-(o-allyloxy-phenoxymethyl)oxazolidinone-2 in particular has pronounced beta-blocking properties.</p>