3,4-dimethylpyridine, 3,5-dimethylpyridine, 2,4-dimethylpyridine, 2,5-dimethylpyridine, 2,6-dimethylpyridine and 2,4,6-trimethylpyridine have been examined by the magnetron technique to determine various parameters of surface ionization. In each case the dependence of lg (the ratio of electron to ion current) upon the reciprocal of filament temperature was examined. Results fall into three distinct groups depending upon the number of methyl groups immediately adjacent to the nitrogen atom. The results are discussed in relation to the proposal that formation of ions is preceded by adsorption of the compound on the filament via the nitrogen atom.