beta-1-Glycoprotein (SP1) concentration of 170 women with undisturbed pregnancy under 18th week were taken as reference. SP1 levels of 72 patients with threatening abortion but favorable outcome were compared with those of 70 patients with threatening abortion and subsequent miscarriage. Decreased SP1 levels were determined in most (88%) patients who aborted, whereas 88.8% of patients with favorable outcome had SP1 levels within normal range. The predictive value of SP1 determination in early pregnancies is emphasized.