Photographic properties of 1-benzyl-1,4-dihydronicotinamide (BNAH) are studied for better understanding of the mechanism of the production of high contrast by the infectious development induced by the combination of a pyridinium salt and Metol-ascorbate developer. Treatment of silver bromide emulsion or silver chlorobromo emulsion by BNAH and redox buffer followed by development gave high fog density. It has been suggested that the oxidation product of BNAH by redox buffer nucleates silver halide grains and makes them developable. Results support the hypothesis that dihydropyridine works as an intermediate in the production of high contrast by the infectious development in the presence of a pyridinium salt.