In most states, political parties can find out who is voting from home and when by buying lists from counties showing the voters' addresses, phone numbers and birth dates.

In the West, online companies buy contacts from cost-per-action (CPA) networks, which are intermediates that buy lists of email addresses from websites with well-defined users.

Don't buy, rent or sell lists.

More often than not, list brokers act as "go-betweens" matching list owners to those who wish to buy or rent lists, receiving a commission from the list owners.

The company also buys outside lists.

Discount companies assemble their networks by buying or leasing lists of medical providers from preferred provider organizations.

Ms. Staub maintained that KeySpan Energy Solutions had simply bought lists of Long Islanders who lived in areas known to have a heavy concentration of gas customers.

Both those companies are turning up on many Wall Street buy lists primarily because they use new technologies.

For less than $1,000 you can buy the software that puts false headers on a document, buy e-mail lists and send out a million e-mails.

One can, however, buy lists of Jewish donors from the organization's list broker, the American List Company.