M2 Medium is a modified form of M16 medium that contains HEPES along with sodium bicarbonate as a buffering agent. Pyruvate and lactate present in the medium serve as energy sources since preimplantation embryos do not utilize glucose efficiently. AL142 contains HEPES buffer, sodium bicarbonate and sodium lactate. It does not contain penicillin and streptomycin. M2 Medium is a modified form of M16 medium that contains HEPES along with sodium bicarbonate as a buffering agent. The presence of HEPES allows collection and handling of preimplantation stage mouse embryos for prolonged periods outside CO2 incubator. Pyruvate and lactate present in the medium serve as energy sources since preimplantation embryos do not utilize glucose efficiently. AL142 contains HEPES buffer, sodium bicarbonate and sodium lactate. It does not contain penicillin and streptomycin.