Broncho‐alveolar cells lavaged from the lungs of 1‐ and 7‐day‐old piglets and adult pigs were examined to determine their alveolar macrophage content, cell size, and ability to phagocytyze emulsified oil droplets and to chemiluminesce in response to opsonized zymosan particles. Alveolar macrophages were identified by specific cytochemical stains and differential cell counts as being 95%, 97%, and 90% of the cell populations, respectively. The cell volume of macrophages from 1‐day‐old pigs was 383 ± 40 µm3; while the cell volumes from 7 day and adult pigs were 1,660 ± 265 and 1,411 ± 310µm3. Alveolar macrophage from 1‐day‐old piglets possessed little ability to engulf oil droplets; however, macrophages from 7‐day‐old piglets phagocytized these opsonized droplets at a rate equivalent to alveolar macrophages obtained from adult pigs. The phagocytosis of oil droplets by both 7‐day and adult alveolar macrophages manifested similar characteristics. Both rates can be described by saturation kinetics, and while temperatures from 37° to 30°C had little effect, the rate declined rapidly between 30° and 16°C. Alveolar macrophages from 1‐day‐old piglets displayed a lower magnitude of chemiluminescence than cells from 7‐ day‐old and adult pigs and did not always respond to zymosan exposure. On the other hand, 7‐day‐old and adult pig alveolar macrophages were quite similar in their ability to chemiluminesce. Increasing extracellular glucose from 1 to 20 mM induced a concomitant increase in chemiluminescence. The findings suggest that functionally competent alveolar macrophages emerge in the pig lung approximately 1 week after birth.