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TORONTO — Seven years ago, Montreal businessman Stan Diamond arranged to index the Jewish records of his ancestral town of Ostrow Mazowiecka, Poland, because he wanted to trace the path of a rare genetic condition within his family tree.

Diamond's goal was medical as well as genealogical, since he sought to alert potential carriers of the beta thalassemia trait of the hazard involved. Offspring of two carriers stand a one-in-four chance of acquiring a blood disease that is always fatal, usually before they are 20.

After tracing his own ancestry back to 1760 and finding and warning many distant relatives with the genetic trait, Diamond realized that a wider indexing project would be a boon for thousands of Jewish genealogists.

"I began to think, 'Wouldn't it be wonderful if we could do this for all of Poland?'" he recalls.

With the help of fellow genealogists Steven Zedeck of Nashua, N.H., and Michael Tobias of Glasgow, Scotland, he became coordinator of the Jewish Records Indexing Project for Poland, which to date has produced an index of 1.8 million vital Jewish records from the 19th century.

The index is easily accessible and searchable on the Internet, where it is consulted by hundreds of researchers every day. The project is on the Web at www.jewishgen.org

The project relies upon a widespread network of hundreds of volunteers whose efforts are coordinated largely over the Internet.

It also employs several Russian-born data-entry clerks in Warsaw. A facility with both Russian and Polish is essential for these workers because the record books were handwritten in Polish until 1868 and in Russian thereafter.

A former manufacturer of decorated ceilings and the president of the Jewish Genealogical Society of Montreal, Diamond estimates that roughly 20 percent of all available Polish-Jewish records have been included in the JRI-Poland database so far.

It is the largest and perhaps the most impressive of about 60 indexing projects accessible via JewishGen, the Internet gateway to Jewish genealogy.

In its six-year existence, JewishGen has experienced explosive growth. The nonprofit communal organization maintains a Web site that is a focal point for daily discussion groups and many volunteer projects, including an effort to post a growing number of searchable databases to the net.