The hitherto unknown phenylpropargylamine derivative 1-(3,5-bistrifluoromethylphenyl)-3-(4-tert-butyl- piperidino)prop-I-yne, and acid addition salts thereof, have been found to be useful as rodenticides. Processes for the preparation of the new phenylpropargylamine derivative by the application of known methods are described and so are suitable rodenticidal compositions.