Combined IR spectroscopy dipole moment and average molecular weight measurements and DFT calculations on the self-aggregation of N N'- and N,N-dialkylureas in solvents of different polarities were, performed It was found that to acquire a better understanding of the mechanisms of associations the simultaneous use of all of these methods is required It was found that symmetric dialkyl derivatives of urea associate much more strongly, giving in CCl4 even a 12-fold mass of monomers in contrast to asymmetric ones where the average molecular weight reaches only a 2-fold mass of monomers The very strong influence of solvents was discovered The aggregation is much weaker in more polar chloroform and 1,2-dichloroethane leading to only a 2-fold increase in the average molecular weight A strong influence of the symmetry of dialkylurea molecules was also found Dipole moments of symmetric N,N'-dialkylurea increase with concentration suggesting a rather linear arrangement of vectors in an aggregate For asymmetric N,N-derivatives dipole moments decrease with concentration DFT calculations were used to predict the form of aggregation