Intersubband polaritons in the THz range are observed by coupling intersubband transitions in parabolic quantum wells to metallic microcavities. The polaritonic states are tuned in frequency by electrically modulating the electron density in the device using a gate. Tuning of 140 Ghz is observed at a lower polariton frequency of 2.5 THz in reflection measurements. Biasing the structure for electroluminescence measurements also modulates the electron density, which can lead to differential electroluminescence line shapes.