The thermal and hydrolytic stabilities at 90 and 120°C of butylN-phenyl urethane, N,N1-diphenylurea, butyl-α,γ-diphenyl allophanate, and 1,3,5-tri-phenylbiuret in 1,4-dioxane containing traces of water were investigated in the presence of dibutyltin dilaurate by HPLC. the stabilities decrease with increasing temperature and are also affected by the presence of water in the system. the rate and equilibrium constants of allophanate and biuret were calculated.