In this study a new heparin-like anticoagulant in the human placenta is described and an extensive review of the literature is given. An anticoagulant with a heparin-like activity was isolated from an extract of the human placenta. A two-stage purification procedure was applied: affinity chromatography on heparin-Sepharose and ion-exchange chromatography on DEAE-trisacryl. The isolated anticoagulant fraction was found to prolong both thrombin clotting time and activated partial thromboplastin time and to increase the activity of antithrombin III and heparin cofactor II. The placental-tissue anticoagulants described in the literature are divided by the author into five groups: (1) acidic peptides of low molecular weight; (2) thrombomodulin; (3) phospholipid-binding protein anticoagulants; (4) heparin-like anticoagulants, and (5) others. The anticoagulant described in the present study has been classified to the 4th group.