Ultrafast relaxation dynamics of light and heavy holes in GaAs following femtosecond valence-to-conduction-band excitation are measured by probing the light- and heavy-to-split-off hole transitions at different midinfrared wavelengths using the recently developed broadly tunable femtosecond optical parametric oscillator. The initial relaxation times are less than 75 fs, and a spectral hole-burning effect is seen. The results suggest that carrier–carrier and optical-phonon scattering, in particular, polar optical-phonon scattering, are the primary processes leading to the initial redistribution of heavy and light holes. ©1998 American Institute of Physics.