The present invention is directed to a process for preparing a cellular polyurethane by reacting with an NCO-reactive component in the presence of a homogeneous mixture of an optionally water-containing adduct of carbon dioxide an amine containing at least one secondary amino group, low primary amino groups and at least one primary or secondary hydroxyl group (provided there are not more primary hydroxyl groups than amino groups), an amine catalyst and optionally monofluorotrichlormethane. The present invention is directed to the homogeneous mixture these three components.