The various recorded methods of synthesizing 10-methylphenothiazine were reviewed, and an improved process is suggested which gives consistent yields of 50–60% purified product. A series of bis-Schiff's bases was prepared by condensation of 3-formyl-10-methylphenothiazine with a number of diamines, and reduction of this series yielded a corresponding series of bis-secondary amines. The secondary amines did not show an NH absorption band in the infrared spectra unless considerably higher than normal concentrations were used, but nuclear magnetic resonance studies in deuteriochloroform confirmed the existence of the ―CH2NH― group. A model compound of the same type (namely, 3-phenyliminomethylene-10-methyl-phenothiazine) was synthesized, and it was found to exhibit exactly the same effects in the infrared spectra and in the nuclear magnetic resonance spectra in deuteriochloroform. In dimethyl sulfoxide-d6, the model compound showed clear evidence of coupling between the NH and the adjacent methylene group, an effect which is rarely seen.Quaternization of the secondary amines was unsuccessful in all but a few cases.