TEN YEARS ago Owren1 described a patient who had a bleeding diathesis attributable to the lack of a single blood-clotting factor, namely, Factor V, or labile factor.* Owren8 designated the disease "parahemophilia," to emphasize the clinical similarity to hemophilia. Including the original report, only 45 definite cases, involving 13 families, have been reported (Table 1). In addition to the definite cases summarized in this table, four presumptive cases have been reported. Rhoads and Fitz-Hugh, in 1941,19 described a 16-year-old boy whose findings were compatible with a deficiency of the labile factor, although their report was made before the labile factor was recognized. The addition of plasma exposed to adsorption by aluminum hydroxide shortened the patient's "prothrombin time" from 93 seconds to 41 seconds, as compared with a shortening from 93 seconds to 27 seconds by the addition of normal plasma. Cosgriff and Leifer,20 in 1952, reported on a 66-year-old man;