hormone that is included in the medium to maintain rates of cell metabolism triiodothyronine is supplemented to the medium at a concentration range between about 0 to about 400 u03c1m more preferably between about 2 u03c1m to about 200 u03c1m and most preferably at about 20 u03c1m either or both ethanolamine and o phosphoryl ethanolamine which are phospholipids are added whose function is an important precursor in the inositol pathway and fatty acid metabolism supplementation of lipids that are normally found in serum is necessary in a serum free medium ethanolamine or o phosphoryl ethanolamine or both are provided to media at a concentration range between about 10 u2212 6 m to about 10 u2212 2 m more preferably at about 1 u00d7 10 u2212 4 m hydrocotisone has been shown to have benefits when culturing other epithelal cell types to promote phenotype and therefore enhance differentiated characteristics rubin et al j cell physiol 138 208 214 1986 hydrocoitisone may be provided at a concentration range of about 0 04 u03bcg ml to about 4 0 u03bcg ml preferably at about 0 4 u03bcg ml selenium is added to serum free media to resupplernent the trace elements of selenium normally provided by serum selenium may be provided at a concentration range of about 10 u2212 9 m to about 10 u2212 7 m most preferably at about 5 3 u00d7 10 u2212 8 m the amino acid l glutamine is present in some nutrient bases and may be added in cases where there is none.