Dispersions of polyurea particles are made by reacting polyisocyanate compounds and coreactants that include at least one polyamine while dispersed in a base polyether. The polyisocyanate or the polyamine, or both, has a functionality of at least 2. A highly preferred coreactant is an alkylthio-substituted aromatic diamine such as 3,5-di(methylthio)-2,4-toluene diamine. The dispersions have extremely small particles, which promotes storage stability.