Molecular motion of 1,6-diphenyl-1,3,5-hexatriene embedded in intact guinea pig alveolar macrophage membranes was investigated by using techniques of nanosecond timeresolved fluorescence anisotropy measurements in the temperature range of 0-50 °C, and as a function of benzyl alcohol concentration. It was shown that molecular arrangement and microheterogeneity of the hydrocarbon region surrounding 1,6-diphenyl-1,3,5-hexatriene molecules are dependent on the temperature and benzyl alcohol concentration. The lipid orientation order parameter, Sv, showed a discontinuity in the temperature range 12-40 °C, which may indicate a phase transition. N-Formylmethionylphenylalanine-stimulated production of O2- from macrophages increased with temperature parallel with changes in Sv. Benzyl alcohol decreases the magnitude of the lipid order parameter at all temperatures studied. In the same concentration range of benzyl alcohol, stimulated O2- production by macrophages was inhibited. These data show the complex relationship between lipid integrity in macrophage membranes and a physiological function of these cells. In addition, the results indicate that benzyl alcohol influences the integrity of both the protein and lipid hydrophobic regions of the membrane.