SUMMARY A system is described in which rhinovirus 2 may be grown in suspension cultures of L 132 ceils. The virus adsorbed to the cells more efficiently at 33 ° than at 4 °, probably by means of specific trypsin-sensitive lipoprotein recep- tors on the cells. Virus penetration demonstrated using a potent virus anti- serum was temperature-sensitive and rapid at 33 ° . During single-cycle virus growth at 33 ° the latent period was about 4 hr and maximum virus yields were obtained about Io hr after infection. Addition of 3 ° mM-MgCI~ in the medium enhanced virus release from the cells but did not affect the total virus yield. Highest virus yields were obtained at pH 7"7 and a temperature of 33 °. Lower temperatures increased the latent period. At higher temperatures up to 37 ° the latent period was shorter and the virus titre ceased to increase earlier. At 39 ° the latent period was longer than at 33 ° and there was a severe inhibition of virus production. Shift-up and shift-down experiments indicated that the temperature-sensitive event or events at 39 ° occurred late in the growth cycle.