The conformational and morphological changes occurring at the air/water interface during the compression of pure poly(D-lactide) (PDLA), pure poly(L-lactide) (PLLA), and their equimolar blend have been thoroughly investigated using polarization-modulation infrared reflection-absorption spectroscopy and Brewster angle microscopy. The results obtained show that the plateau region observed in the isotherm of the pure polylactides corresponds to an equilibrium between free 10(3) helices in a fluid phase and 10(3) helices in unstable solidlike domains. For the blend, this plateau corresponds to an equilibrium between free 10(3) helices in the fluid phase, 10(3) helices in unstable solidlike domains of pure polyenantiomers, and 3(1) helices in very stable solidlike domains of the PDLA/PLLA stereocomplex. The results obtained also suggest that the proportion of stereocomplex and pure polyenantiomers domains formed during the compression of the monolayer of the blend can be modulated by different experimental parameters such as the molecular weight of the polymers, the subphase temperature, the compression rate, and the "incubation" time.