Opti-MEM® I Reduced-Serum Medium is an improved Minimal Essential Medium (MEM) that allows for a reduction of Fetal Bovine Serum supplementation by at least 50% with no change in growth rate or morphology. Opti-MEM® I medium is also recommended for use with cationic lipid transfection reagents, such as Lipofectamine™ reagent. Opti-MEM® I medium can be used with a variety of suspension and adherent mammalian cells, including Sp2, AE-1, CHO, BHK-21, HEK, and primary fibroblasts.