As previous sequential and structural analyses showed its conserved homology to members of the galectin superfamily, Placental Protein 13 (PP13) was designated galectin-13. Similarly to eosinophil Charcot Leyden Crystal protein / galectin-10, its weak lysophospholipase activity was proved. Sugar binding assays revealed that residues widely expressed in placenta had the strongest binding affinity to PP13, which expression was found to be restricted to placenta. With regard to its strong labeling of the syncythiotrophoblasts’ brush border membrane as well as its co-localization and specific binding to annexin II, PP13 was assumed to be externalized to the cell surface like other galectins. In a comparative study we found, that in the 3rd trimester, expression of PP13 was significantly reduced in preeclamptic (n = 20) and HELLP syndrome (n = 5) placentas compared to gestational age matched healthy samples (n = 25). In the same pathologic cases, maternal PP13 serum levels were also lower than in controls. Recently, PP13 was also successfully tested as a new 1st and 2nd trimester placental marker for the prediction of preeclampsia and IUGR. With regard to these results, PP13 may have special immunobiological function at the lining of the common feto-maternal blood-paces. The possible clinical importance of PP13 in pathological pregnancies with immunological background have to be emphasized.