Infrared-microwave-microwave triple resonance experiments in ammonia are reported. The power modulated P13 line of a N 2 O laser was used to pump the ν 2 [Q(8,7)] transition of ammonia. The dependance of the intensity of the collisionally induced signals produced at the (7,7), (6,6), (5,5) and (4,4) microwave transitions on c. w. microwave power applied to the (8,7) transition was measured. From the null signal observed for the (7,7) transition when the (8,7) transition was saturated, it was concluded that population changes produced in the (7,7) levels occur predominently via direct collisional transitions which are strongly parity sensitive and that other processes have little contribution. The signals observed for the (6,6), (5,5) and (4,4) are produced by processes which are largely insensitive to parity.