The electroreflectance and absorption spectra as well as the hydrostatic pressure dependence of the fundamental absorption edge of GeS, GeSe, SnS, and SnSe crystals are investigated in polarized light. The lowest direct energy gaps are found to be 1V1— 1V1 (E | | a) and 1Λ4— 1Λ4 (E || b) for Ge and Sn monochalcogenides, respectively. The pressure coefficient of the energy gap 1Λ4— 1Λ4 dE/AP = = — (1.3 ± 0.1) × 10−4 eV/MPa of SnSe and SnS is almost twice larger than that of the gap 1V1— 1V1 in GeSe, GeS, and SnSe. On the basis of these investigations, different absorption mechanisms responsible for the fundamental absorption edge are discussed.