An investigation on placenta proteins has been carried out by matrix-assisted laser desorption/ionization (MALDI) ion imaging (II) experiments. This was performed by laser irradiation of the maternal and fetal sides of placenta tissue. To investigate the possible changes in protein profile due to the development of gestational diabetes mellitus (GDM), five placenta samples from GDM patients and five placenta samples from healthy pregnant women were analyzed. An extensive optimization of the tissue slice treatment and of the matrix deposition method was performed. As already observed in MALDI spectra of placenta homogenates, and also in the MALDI-II condition, the most abundant peaks are due to hemoglobin α chain, hemoglobin β chain and hemoglobin γ chain. However, higher molecular weight protein species were detected in the m/z range 20,000-47,000. The species at m/z 30335, m/z 31235 and m/z 32000 show some differences in their abundance in the maternal and fetal sides of the tissue in both classes of subjects under investigation. Comparison with the literature data suggest that they can result from the presence of mitochondrial proteins at tissue level.