A recently developed protein spreading technique, using a subphase of higher density than that of the injected protein solution, was combined with the lipid monolayer approach for two-dimensional crystallization experiments of human C-reactive protein (hCRP) at the air-water interface. Densely packed two-dimensional arrays of hCRP adsorbed on a stearylamine/egg yolk phosphatidylcholine lipid layer have been obtained in the pH range from 5.4 to 5.8. Correct choices of the lipid mixture and of the pH of the subphase were important for the formation of large arrays. Image analysis of transmission electron micrographs showed that the densely packed arrays do not possess crystalline order. The orientational homogeneity of the protein molecules adsorbed on the lipid layer could be used, however, to facilitate single particle averaging techniques. At a resolution of about 1.5 nm a clear handedness of the five-fold symmetric molecule becomes visible, and an asymmetric mass distribution of each subunit is revealed.