Abstract The distribution of bacteriophage T2, adenovirus, and ECHO virus prototype 7 and 19 in aqueous two-phase systems of sodium dextran sulfate, methylcellulose, polyvinyl alcohol, and polyethylene glycol is described. By using a phase system in one step, the virus particles may be concentrated 10–100 times. By using two-step procedures a concentration effect of about 1000 times has been demonstrated. The phase systems have been applied for the isolation of highly pure phage T2 preparations from 2-liter cultures. A procedure for the purification and concentration of ECHO virus from 5-liter cultures is also described. An ECHO virus preparation having a TCD 50 titer of 10 10 to 10 11 per milliliter and a specific activity of 10 13 TCD 50 per gram protein has been obtained. The preparations of phage T2 and ECHO virus have been analyzed in the electron microscope and in the ultracentrifuge. Techniques for the removal of the phase polymers from the virus suspensions are also described.