Solutions in any media of basic salts of N - substitution products of p-amino benzene sulphonamide, e.g. sulphanilamide, sulphapyridine, sulphaguanidine, sulphathiazole and sulphadiazine, are stabilised against the action of oxygen and light by adding an agent capable of supplying sulphite ions, e.g. sodium sulphite as protective agent, which has substantially the same pH as the solution to be stabilised. The solution of the basic salt, which may have a concentration up to 10 per cent may have mono- or poly-hydric alcohols and/or aromatic aldehydes such as, glycerine, isopropyl alcohol, benzyl alcohol, benzaldehyde and normal or secondary butyl alcohols, incorporated providing a mutually protective system with the sulphite.  An additional amount of glycerine up to 10 per cent may be added as a wetting agent.  In order to use the stabilised solution for physiological purposes, it is inadvisable that the pH of the entire solution should rise above 11.  Examples relate to stabilised solutions of sodium sulphathiazole comprising 5 per cent (or 2.5 per cent) sodium sulphathiazole, more than 0.5 per cent sodium sulphite, e.g. 2 per cent sodium sulphite, more than 1 per cent, e.g. 5 per cent (or 3 per cent) glycerine, water and colouring and sodium phosphite if desired.  The salts may be admixed dry into pellets to give the desired solution when mixed with water.  The stabilised solution may be obtained in the form of a jelly by incorporating methyl cellulose containing preferably as a preservative sodium benzoate.  The sodium sulphthiazole employed in the examples above may be replaced by sodium sulphadiazine.ALSO:Therapeutic solutions in any media of basic salts of N, -substitution products of p-amino benzene sulphonamide, e.g., sulphanilamide, sulphapyridine, sulphaguanidine, sulphathiazole and sulphadiazine, are stabilized against the action of oxygen and light by adding an agent capable of supplying sulphite ions, e.g., sodium sulphite as protective agent, which has substantially the same pH as the solution to be stabilized. The solution of the basic salt, which may have a concentration up to 10 per cent. may have mono- or poly-hydric alcohols and/or aromatic aldehydes such as, glycerine, isopropyl alcohol, benzyl alcohol, benzaldehyde and normal or secondary butyl alcohols, incorporated providing a mutually protective system with the sulphite.  An additional amount of glycerine up to 10 per cent. may be added as a wetting agent.  In order to use the stabilized solution for physiological purposes, it is inadvisable that the pH of the entire solution should rise above 11.  Examples relate to stabilized solutions of sodium sulphathiazole comprising 5 per cent. (or 2.5 per cent.) sodium sulphathiazole, more than 0.5 per cent. sodium sulphite, e.g., 2 per cent. sodium sulphite, more than 1 per cent., e.g., 5 per cent. (or 3 per cent.) glycerine water and coloring and sodium phosphite if desired.  The salts may be admixed dry into pellets to give the desired solution when mixed with water.  The stabilized solution may be obtained in the form of a jelly by incorporating methyl cellulose containing preferably as a preservative sodium benzoate.  The sodium sulphthiazole employed in the examples above may be replaced by sodium sulph-diazine.