Morphological changes in the coexistence region of monolayers of L-alpha-dipalmitoylphosphatidyl choline (DPPC) with different spreading concentration have been investigated by Brewster angle microscopy (BAM). At low spreading concentration (<0.05 mM), domains of compact shape have been observed. At concentration (C) > 0.05 mh? the domain size was enlarged and the shape was getting well developed. At C = 10 mM DPPC formed mixed triskelions and S-shaped domains. The adsorption isotherm of DPPC at the water/chloroform interface indicates that DPPC starts to aggregate in chloroform at C > 0.03 mM and the surface tension does not change with further increased concentration. Results from BAM show that the domain structures are influenced by impurities rather than by the initial aggregation of DPPC molecules in the spreading solvent chloroform.