Non-resonant femtosecond time-resolved four-wave mixing (FWM) data on gas phase NO2 and N2O4 are presented. The initial rotational dephasing is observed during the first picosecond after excitation. Fast vibrational dynamics (average value 133 +/- 1 fs beats) are observed for dinitrogen tetroxide and are assigned to the nu (3) N-N stretching mode in the ground state ((1)A(g)). Rotational revivals on the picosecond time scale are recorded for both samples. No evidence of a long-lived excited state participation was found using photon echo (PE) or virtual echo (VE) pulse sequences with 800 nm laser pulses, however, NO2 photoproducts were observed following N2O4 excitation.