At the temperature of the distal airways (37uC), the growth kinetics and mean peak titers of A/Victoria/3/75 and A/Dk/ Eng/62 reached 2.3610 8 pfu/ml and 4.7610 7 pfu/ml, respectively, by 48 hours post-inoculation (hrs pi) ( Figure 1A ). At the temperature of the proximal airways (32uC), A/Victoria/3/75 showed a modest delay in replication but still reached maximal titer of 7.8610 7 pfu/ml by 48 hrs pi. In contrast, A/Dk/Eng/62 grew very slowly, with yields at time points up to 48 hrs pi reduced by 3 to 5 logs compared to growth for this virus at 37uC or A/ Victoria/3/75 at either temperature.