Contains HEPES buffer, 2,400 mg/L sodium bicarbonate, hypoxanthine, thymidine, sodium pyruvate, L-glutamine, trace elements, growth factors, and phenol red reduced to 1.1 mg/L. Opti-MEM® I is a modification of Eagles Minimum Essential Medium, buffered with HEPES and sodium bicarbonate (2.4 g/L) and supplemented with hypoxanthine, thymidine, sodium pyruvate, L-glutamine, trace elements, and growth factors. The concentration of phenol red has been reduced to 1.1 mg/L. Most cells routinely cultured in serum-supplemented medium may be transferred directly into Opti-MEM® I with a minimum of 50% reduction in serum. Further significant reductions in serum requirements have been achieved with myelomas (Sp2/O-Ag14, P3~63 Ag8.653, P3-NSI-Ag4-1) and derived hybridomas, as well as with fibroblasts and epithelial cells of both normal and tumor origins. For very low serum supplementation (<1%) with attachment-dependent cells, add 500 to 1,000 mg/L calcium chloride. Ideal for use during cationic lipid transfections.