The present invention provides a method for preparing aqueous extracts of vegetals, particularly of plants, which comprises the steps of a) decontamination of the plant, b) comminuting the plant, c) treatment of the comminuted plant with a laser radiation, d) suspension of the mixture obtained in step c) in water, e) maceration of the suspension obtained in step d), and f) separation of the resulting liquid. The invention also provides the compositions obtained by the present method, some of which find application in medicine, particularly in the treatment of immune-suppressant diseases such as cancer, tuberculosis, influenza, common cold and AIDS, or in the treatment of viral diseases such as hepatitis.