To provide an injectable formulation for treatment of neoplastic disease and the like improving stability of an immune response modifier compound (IRM compound) in the formulation as well as physical stability of the formulation itself, where the formulation can be stored for long periods of time (>6 months) and at temperatures ranging from 5癈 to 40癈.SOLUTION : Injectable formulations comprise ethanol, refined sesame oil, and an IRM compound. Preferably, the IRM compound is N-(4-{[4-amino-2-butyl-1H-imidazo[4, 5-c]quinolin-1-yl]oxy}butyl)octadecanamide, or a pharmaceutically acceptable salt thereof.SELECTED DRAWING : None