To the Editor.— In a recent report,1clearing of plaque-stage lesions in five patients with mycosis fungoides with the topical application of several nitrosourea solutions was described. Since the submission of that report, four additional cases have responded favorably to topical applications of 0.05% aqueous and alcoholic solutions of 1-(2-chloroethyl)-1-nitrosourea (NSC 47547). In that communication data as to the stability of the solutions was incomplete. We here present further data as to the stability of NSC 47547, 1-methyl-1-nitrosourea (NSC 23909), and 1,3-bis(2-chloroethyl)-1-nitrosourea (carmustine [BCNU]) in absolute and 95% alcohol and in distilled water under refrigerated conditions (0 to 5C). The method was by ultraviolet absorption using a spectrophotometer at 230-nm (carmustine) and 232-nm (NSC 47547 and NSC 23909) wavelengths. The concentration range was from 0.5 to 0.6 mg/ml (0.05% to 0.06%) which was the most common strength used in treatment. The total period of observation was three months. All