We examined alveolar type II cells and extracellular surfactant (tubular myelin) of human lungs and compared them with those of experimental animals (mouse, rat and dog) using a freeze-fracture technique for electron microscopy. Lamellar bodies (intracellular surfactant) in alveolar type II cells of human lung showed features different from those of the experimental animal lungs. Namely, multicentric foci of lamellae, an amorphous portion with some degree of lattice-like structure in the mature bodies, unpaired split membranes of lamellae and also our previously reported connection of the lamellar bodies to the endoplasmic reticulum (Am. Rev. resp. Dis. 127: 1983) were found in alveolar type II cells of human lungs but not in type II cells of experimental animal lungs. On the other hand, there were no differences noted in extracellular surfactant between human and experimental animal lungs. These findings indicate the possibility that a mode of surfactant production and/or storage in alveolar type II cells exists in human lung which is different from that in experimental animal lungs.