Different commercially available peptone preparations, all derived by enzymatic digestion of meat, were tested for their ability to replace the individual amino acids and polyethylene glycol (PEG)-treated serum in BHK suspended cell culture growth medium. Cell growth was not impaired if the individual amino acids were replaced by 3 g/l of peptone in combination with 3 g/l LAH and 5% PEG-treated bovine serum. The concentration of the latter could be reduced to 1% by gradually lowering the concentration in successive cell passages. No significant differences in growth stimulating properties were observed between the peptone preparations. The virus produced was concentrated and partly purified by precipitation with PEG, collection of the precipitate by filter-aid filtration and direct elution from filter cake in the filter by pumping one tenth the original volume of buffer through the filter. The whole procedure was performed in a simple closed system, offering maximum guarantee of bacteriological sterility and preventing virus aerosol formation in the surroundings.