A simple and inexpensive method for the freezing of human blood lymphocytes at −80 C is described. Lymphocytes were frozen in either polystyrene tubes or polyolefin bags. Optimal recovery of cells was obtained when 5 per cent DM SO and 62 per cent plasma were used as cryoprotectants. Viable cell recovery, as assessed by response to phytohemagglutinin (PHA) and pokeweed mitogen (PWM), was greater than 80 per cent after 60 days of storage. In addition, percentages of T and B lymphocytes were essentially unchanged. The excellent viable cell recovery in polyolefin bags suggests that it is possible to cryopreserve large numbers of lymphocytes in a single containe