The phagocytic function of alveolar macrophages obtained from rabbits after they were given sublethal shock by tumbling in a modified Noble-Collip drum was studied. As compared to the phagocytic function of alveolar macrophages from normal rabbits, tumbling produced a statistically significant reduction in vitro bactericidal capacity for bothPseudomonas aeruginosaandEscherichia coli. However, there was no alteration in the ingestive phase. The reduced bactericidal capacity was evident within 15 minutes after the stress, but the batericidal capacity had returned to normal in rabbits that were allowed to recover for 24 hours before the studies were performed.