Densities, refractive indices, viscosities, dielectric constants and the absorptions of several solvatochromic indicators have been determined at 25°C for mixtures of N,N′-dimethyl-N,N′-propyleneurea (DMPU) and water in the complete mole fraction scale. the results are compared with the properties of hexamethylphosphotriamide (HMPT) and its mixtures with water which show a striking similarity to DMPU and its mixtures with water. Since HMPT was found to be carcinogenic in animal tests, DMPU offers a suitable substitute since it may be regarded as safe under laboratory condit