A lowering of the development temperature introduces development defects which are characterized by the partial or total destruction of the developed image and by a deep coloration of the emulsion. These defects are eliminated by increasing the sodium sulfite concentration of the developer. Up to now contrast in nuclear emulsions has been evaluated subjectively by the experimenter; this forbids any comparison of the results obtained in different laboratories.This paper shows that to develop reliably at low temperatures with the usual developers, it becomes necessary to increase the ratio (Na2SO3)/(Amidol). For development temperatures of 10–15°C the concentration ratio needs to be 70% greater than the ones commonly used.A study of track and fog grain properties is carried out. It is shown that at a given temperature the mean gap length is practically independent of the development parameters. The optimum conditions at 14°C are determined with the help of a new quantity termed ``track visibility'' (K), a track to fog signal, and defined byK=blob length×track grain diameter/fog density×(fog grain diameter)2.