Because the presence of serum in cell culture raises safety problems for the production of biologicals, we have developed a serum-free medium (SFM) for the cryopreservation of animal cells. This medium is based of the SFM MDSS2, to which 10% dimethylsulfoxide (DMSO) and 0.1% methylcellulose or 3% polyvinyl pyrrolidone or no other additive than DMSO were added. Both, Vero and BHK-21 cells regularly cultivated in MDSS2, could be cryopreserved in the three serum-free freezing media and could be thawed without any cell loss. No differences could be found between the cells in the standard freezing medium (DMEM containing 10% fetal calf serum and 10% DMSO) and those frozen in SFM, with respect to cell growth and viability. In the case of the Vero cells no differences were observed with respect to their attachment. This medium represents the last step in fulfilling a complete serum-free animal cell based bioprocess.