A STABLE INJECTION OF AN INDOLYLALIPHATIC ACID DERIVATIVE SUCH AS N-(P-CHLOROBENZOLY)-2-METHYL-5-METHOXY-3-INDOLYLACETIC ACID, N-CINNAMOLY-2-METHYL-5-METHOXY-3-INDOLYLACETIC ACID OR N-NICOTINOYL-2-METHYL-5-METHOXY-3INDOLYLACETIC ACID IS PREPARED BY DISSOLVING THE INDOLYLALIPHATIC ACID DERIVATIVE IN A NON-AQUEOUS ORGANIC SOLVENT FOR INJECTION AND ADDING AN AQUEOUS ORGANIC AMINE SOLUTION CONTAINING 0.6 TO 1 MOLE OF SAID ORGANIC AMINE PER 1 MOLE OF THE INDOLYLALIPHATIC ACID DERIVATIVE TO THE RESULTANT SOLUTION. THE THUS OBTAINED INJECTION IS USED AS AN ANTI-INFLAMMATORY DRUG.