The purpose of this investigation was to find out whether long-term treatment of male and female mice with saccharin sodium, sodium cyclamate or cyclohexylamine sulfate, would reduce fertility or induce dominant lethal mutations. Before mating, saccharin sodium or sodium cyclamate were added to the food in a concentration of 1%, while cyclohexylamine sulfate was added in a concentration of 0.11% for at least 10 weeks. This treatment corresponded, in the case of saccharin sodium and sodium cyclamate, to an active substance intake of approx. 2000 mg/kg per day and for cyclohexylamine sulfate to an intake of approx. 200 mg/kg per day (corresponding to approx. 136 mg cyclohexylamine per kilogram per day). These doses affected neither the females nor the males in respect of appearance, behaviour, and weight gain. The doses were also compatible with the normal fertility of the animals. Furthermore, in all cases the treatment did not cause a biologically important increase of pre-implantative and post-implantative losses. The dominant lethal tests did not indicate a mutagenic action of saccharin sodium or sodium cyclamate (1% in the food) and of cyclohexylamine sulfate (0.11% in the food) after 10 weeks' treatment of male and female mice. These results, obtained after long-term treatment, corresponded generally to the findin