We report optical-absorption measurements in high-quality GaSb-AlSb superlattices. The spectra exhibit the two-dimensional density of states and free-exciton peaks. The effect of strain induced by the lattice mismatch is manifested by the anomalous energies of the absorption edges and the reversal of the heavy-and light-hole exciton positions. The data are in good agreement with a simple effective-mass theory. © 1984 The American Physical Society.