The invention refers to the medicinal remedies for respiratory system diseases treatment and may be applied as a substance, capable of restoring respiratory organs functions and used for treatment of different forms of lung pathology. There is proposed a biologically active new tetrapeptide alanyl-glutamyl-aspartyl-leucine of the general formula Ala-Glu-Asp-Leu, capable of restoring respiratory organs function. There is proposed a pharmaceutical substance, containing as an active peptide agent an effective amount of tetrapeptide alanyl-glutamyl-aspartyl-leucine of the general formula Ala-Glu-Asp-Leu, which if used in the medical preparation contributes to the restoration of the respiratory organs function.