Interband magnetophotoconductive spectroscopy was used to determine the reduced masses of several optical transitions in an InAs1-xSbx/In1-xGaxAs strained-layer superlattice and a superlattice constituent, InAs1-xSbx alloy (x approximate to 0.1). In both the alloy and the superlattice, light and heavy hole transitions were identified. From the light-heavy hole splitting in the superlattice, we estimate the valence band offset and find type I behavior. Effective masses and band gap energy are measured for the CuPt ordered alloy. (C) 1995 American Institute of Physics.