Recombinant human serum albumin (rHSA) was produced by genetically transformed Pichia pastoris yeast. The cell-culture supernatant (CCS) contained 8-12 g/l rHSA that was purified in a three-step procedure involving (1) a capture step using the newly developed cation exchanger Capto (TM) MMC; (2) an intermediate step using Phenyl Sepharose (TM) and, (3) a polishing step using Aminobutyl Sepharose (TM) 6 FF. The total recovery was 25-35% and the product fulfils the purity criteria of the European Pharmacopeia. Purified rHSA and plasma-derived HSA were essentially identical judging by SDS- or native-PAGE, and the pigment level (expressed as A(350)/A(280)) in the rHSA was 0.03 or less and was strongly dependent on the quality of the CCS. Dimers and polymers in the final product were less than that found in purified plasma-derived HSA. The molar mass of the purified rHSA, as well as of its natural counterpart, is 67 000 Daltons by MALDI-ToF mass spectrometry, while the iso-electric points of both recombinant and natural HSA ranged between pH 5.42-5.55 when determined in 8 M urea. The stability profiles of both proteins after heat treatment were identical as determined by differential scanning calorimetry (DSC). The results obtained here suggest the purified rHSA to be a homogeneous protein identical to its natural counterpart.