Simultaneous waves, resonant particle, and ambient plasma data from Ogo 5 for chorus emissions on August 15, 1968, were found consistent with the theoretical critical pitch angle anisotropy condition for whistler mode instability by Doppler-shifted electron cyclotron resonance. Local generation, as determined by wave normal measurements, occurred only when the pitch angle anisotropy of resonant electrons required for instability substantially exceeded the critical anisotropy defined by Kennel and Petschek (1966).