Flexible polyurethane foams are produced by reacting a polyol and a polyisocyanate in the presence of a catalysts and other auxiliary agents, the process characterized in that a tin-based catalyst is not used. One process includes reacting a polyether polyol containing at least 5% by weight of an oxyethylene group in the chain and having a terminal secondary OH group, a toluene diisocyanate and/or a derivative, and one or more specified imidazole compounds, the process conducted in the absence of a tin-based catalyst.