The specialty of perinatology has blossomed and burgeoned during the past few years and has brought together a health team of obstetricians, neonatologists-perinatologists (nepediatricians), clinical nursing specialists, and technicians whose primary concern is the pregnant mother and her newly born infant. This symbiotic unit has special medical problems, and a firm understanding of the physiology and pathophysiology of interacting systems has obvious merit for those charged with its care. Thus, it is appropriate that two authorities in the field, Dr William Hathaway, a pediatric hematologist whose major contributions have been in the field of neonatal coagulation, and Dr John Bonnar, an obstetrician-gynecologist with a particular interest in hemostasis during pregnancy, have collaborated in preparing this interesting monograph. A common problem in any perinatal center today is the 1,100 g premature infant with respiratory distress syndrome and ecchymoses, oozing from puncture sites, thrombocytopenia, prolonged prothrombin time (PT) and partial thromboplastin