Iscove's Modified Dulbecco's Medium is an enriched modification of Dulbecco's Modified Eagle's Medium wherein serum can be partially or totally replaced by chemically defined substances. Iscove's Modified Dulbecco's Medium does not contain L-glutamine, HEPES buffer and phenol red. Iscove's Modified Dulbecco's Medium is an enriched modification of Dulbecco's Modified Eagle's Medium wherein serum can be partially or totally replaced by chemically defined substances. The medium contains additional amino acids, sodium selenite, sodium pyruvate, vitamins and inorganic salts. Potassium nitrate is substituted by ferric nitrate. IMDM was the first medium utilizing HEPES buffer. The medium when appropriately supplemented supports good growth of precursor cells of erythrocytes and macrophages. The medium also supports good growth of T and B lymphocytes and a variety of hybrid cells under serum free or reduced serum conditions. AT261A is Iscove's Modified Dulbecco's Medium. It does not contain L-glutamine, HEPES buffer and phenol red.