RPMI 1640 Medium was originally developed by Moore and his colleagues at Roswell Park Memorial Institute (RPMI). It was based on the RPMI 1630 line of media which utilized a bicarbonate buffering system and alterations in the amounts of amino acids and vitamins. A Dutch Modification of RPMI 1640 is also available through MP. The Dutch Modification contains 6400 mg/L sodium chloride instead of 6000 mg/L, 1000 mg/L sodium bicarbonate instead of 2000 mg/L, and 20 mM HEPES. RPMI has successfully been used for the cultivation of normal human and neoplastic leukocytes. It is now a popular general purpose medium when properly supplemented. As a modification of McCoys 5A Medium, it was formulated to support lymphoblastoid cells in suspension culture, but it has since been shown to support a wide variety of cells that are anchorage dependent. Originally intended to be used with a serum supplement, RPMI 1640 has been shown to support several cell lines in the absence of serum. It has also been widely used in fusion protocols and in the growth of hybrid cells.