Summary Human pulmonary alveolar macrophages (PAMs) were cultured for 24–72 h with varying concentrations (0–300 μg/ml) of amosite asbestos (AS). At lower AS concentrations, (< 100 μg/ml) no decrease in cell viability occurred during the first 24 h of culture. Significant cytotoxicity ( P < 0.005 in all instances) was observed, however, following incubation for 24 h with higher AS concentrations (> 100 μg/ml). Even following incubation with lower concentrations of AS, significant cytotoxicity ( P < 0.006 in all instances) was observed after 48 or 72 h of culture. Scanning electron microscopy (SEM) clearly illustrates the various stages of AS phagocytosis by PAMs. SEM also documented morphological changes in PAMs following AS exposure. These included increased zeiosis and the appearance of a fibrous-like material on the surface of AS fibers following initial contact with the PAM cytoplasmic membrane. Further study of the biological interactions between AS and human cells, such as PAMs, might provide valuable information regarding the etiology of AS-related lung disorders.