Aqueous dispersions of dipalmitoyl phosphatidylcholine (DPPC), calf lung surfactant (LS) and an organic solvent extract of calf surfactant (CLSE) were examined by Fourier transform infrared (FTIR) spectroscopy in the presence and absence of calcium. DPPC, the single most abundant constituent of lung surfactant, had FTIR spectra that were essentially equivalent in 0.15 M NaCl with or without calcium (5 mM CaCl2 or 5 mM EDTA at pH similar to 5.6). DPPC dispersions had spectral characteristics very similar to solid DPPC, with differences reflecting largely phosphate group hydrogen bonding in the aqueous phase. In contrast, dispersions of CLSE and whole LS had spectral behavior that was calcium-dependent. In the absence of calcium, acyl wagging bands (similar to 1170-1300 cm(-1)) were significantly decreased in intensity for CLSE compared to DPPC, indicating that the hydrophobic surfactant proteins and secondary surfactant lipids led to fewer phospholipid chains in the trans configuration. Wagging bands were also decreased in LS without calcium compared to DPPC. Phospholipid order was increased in dispersions of both CLSE and LS in 5 mM CaCl2 compared to 5 mM EDTA. Acyl wagging bands became more prominent for both CLSE and whole LS with calcium, although they were still less intense than for DPPC alone. Acyl stretching bands in the region 2800-3000 cm(-1) were broadened and lowered in frequency for CLSE in 5 mM CaCl2 compared to 5 mM EDTA, also consistent with increased chain order. Additional calcium-dependent SP-A mediated ordering was indicated by even broader symmetrical and asymmetrical acyl stretching bands for whole LS in 5 mM CaCl2. Broadening of phosphate asymmetrical and symmetrical stretching bands(similar to 1220 and 1080/1065 cm(-1), respectively) for CLSE and LS dispersions in 5 mM CaCl2 suggested that calcium also interacted with at least a subset of surfactant phospholipids in the headgroup region, The observed effects on molecular order from the surfactant apoproteins and secondary lipids in LS and CLSE dispersions may be related to their actions in facilitating the adsorption of DPPC to the air-water interface.