Got a king in your blood? If you can trace back to John of Gaunt, or his father, King Edward III of England, you may ``share the same basic royal heritage as the most noble knight.'' That's what Roderick W. Stuart says in the introduction to his second edition of ``Royalty for Commoners,'' recently issued by Genealogical Publishing Company. The book documents the complete known genealogy of John of Gaunt. According to the publisher of ``Plantagenet Ancestry'' by G. Andrews Moriarty, ``King Edward III (John of Gaunt's father) is the latest king from whom a large number of Americans can claim descent,'' the book's introduction reports. ``His American posterity numbers in the millions...His grandfather, King Edward I...has tens of millions of additional American descendants.'' Mr. Stuart says that ``typically, the American descendant has several colonial ancestors, one or more of whom can be traced to European beginnings. With a little luck and a lot of hard work, the researcher can link his family to that of John of Gaunt. Reading genealogical literature is the key that unlocks the door to this accomplishment and there are hundreds of books, fortunately some still in print, that will be helpful in getting one started.'' Two such texts, ``Ancestral Roots of Sixty Colonists'' (1990), and ``The Magna Charta Sureties'' (1991), both by Frederick Lewis Weis, have been reviewed here and are still in print. ``Royalty for Commoners'' documents more than 400 lines connected to John of Gaunt and spread throughout Europe. Some go back to Roman consuls of the fourth century A.D. The book reads like a Who's Who of European royalty before 1340, when John of Gaunt was born. The genealogy itself takes up 275 of the book's 412 pages, and includes extensive citations. The bibliography alone requires more than 40 pages, and the complete index takes up 70 more pages. Mr. Stuart has over 30 years researching and compiling the information. He himself warns, however, that ``medieval genealogy is murky,'' and he cites a noted American scholar as saying, ``Connections to the ancient world are tentative, many pedigrees before 1200 or so are often speculative, charters and other evidence can be variously interpreted or misinterpreted, even the greatest scholars often make mistakes, and compilers sifting among available printed sources by necessity work at third hand.'' Given that caveat, anyone interested in European royalty connections will find this book, carefully updated from the 1988 edition, an extensive and invaluable source. Copies of the hardcover edition should be arriving in better libraries, genealogy bookstores and genealogical society sales offices, or may be ordered directly at $30 plus $3 postage and handling from Genealogical Publishing Company, Dept. SM, 1001 North Calvert Street, Baltimore, Md., 21202-3897 (1-800-296-6687). --J.F.S.