We obtained a single serum P measurement in 70 subjects at risk for an EP. Retrospectively, a P less than 15 ng/ml was 100% predictive of either an EP or otherwise nonviable IUP, while P greater than 15 ng/ml would have ruled out an EP in all cases. Because of this high degree of diagnostic accuracy, we speculated on the clinical utility of an outpatient D and C for those patients in our series having a P less than 15 ng/ml. Laparoscopy would be reserved for those cases without identifiable chorionic villi on frozen section of curettings. Following this course of management could have potentially diagnosed all EPs at the first ER visit without disruption of a single normal IUP in our series. This sequence could have expedited the diagnosis of EP by up to 14 days compared with a standard hCG/US protocol. This report describes a promising new test for the early detection of EP. The findings, however, require confirmation in a prospective trial before widespread clinical implementation.