Free-Wilson technique with the use of computer correlation-regression and dispersion analysis program made it possible to determine the importance of certain radicals and functional groups for the characteristics of the toxicity of phenylurea compounds. Specific contribution of different functional groups depending on their position in the molecule to the values of toxicometric indices (LD50, Limac, Limch) and MAC of those compounds in the air of the working area were determined. Summary contributions of radicals with their functional groups to the values of toxicity indices and MACs for individual substances of the phenylurea group was calculated. A possibility was shown to use the Free-Wilson technique for the rapid prediction of toxicity and hygienic standards for new phenylurea compounds in the air of the working area.