Insect-XPRESS Medium is a protein-free formulation designed to support the growth of insect cell lines derived from Spodoptera frugiperda (Sf9 and Sf21) and Drosophila melangaster (S2). Cell densities in excess of 8.3 × 106 cells/ml can be achieved with suspension cultures of Sf9 cells using Insect-XPRESS Medium and an excess of oxygen. This formulation can also be used for stationary monolayer cultures and shake-flask cultures.