Proteins, which are elevated in their blood concentration in pregnant women and patients suffering from malignant tumours, are reported because of their growing significance for the clinical practice. At present mainly are the following "pregnancy" proteins of clinical relevance: human chorionic gonadotrophin (HCG), human placental lactogen (HPL), placental heatstable alkaline phosphatase (HAP), pegnancy-associated alpha2-glycoprotein ("pregnancy zone" protein, PZ), socalled pregnancy-specific beta1-glycoprotein (SP1) and alpha1-fetoprotein (AFP). Applications to the clinical practice may be the surveillance of normal pregnancy, the recognition of dangerous conditions for mother and fetus, the inhibition of graft rejection, the induction of abortion, antibodies against pregnancy proteins as abortifacient and antifertilizer as well as the tumour diagnosis including the control of treatment and recognition of recidives.