Affluent people are increasingly likely to use the Internet to make their charitable donations, a new survey of nearly 3,500 donors has found.

But charities are turning off some of their biggest donors — people who give $1,000 or more, the survey found. Some charities send too many messages to donors who say they don't want them, while others don't take advantage of the interest many donors express in expanding their online interaction with nonprofit organizations, the survey found.

"Most charities are not paying attention," says Mark Rovner, president of Sea Change Strategies, a fund-raising consulting company in Takoma Park, Md. "The people responsible for [soliciting] larger gifts need to start taking the Internet much more seriously than they have."

Sea Change conducted the survey along with Convio, an Austin, Tex., company that provides Web-based software for nonprofit groups, and Edge Research in Arlington, Va., which does research and polling for nonprofit organizations.

The survey, which was conducted online, was based on data from 3,443 donors who had made gifts of at least $1,000 to a single cause in the past 18 months and donated an average of more than $10,896 per year to charities. Sixty-four percent of the donors were age 45 to 64, and 57 percent had incomes of at least $100,000. The donors' names were provided by 23 organizations that represent an array of causes, including advocacy groups, health organizations, international relief groups, public television stations, and Christian ministries.

Among the key findings:

• Four out of five donors said they had made a charitable gift online, and a little more than half, 51 percent, said they prefer to use the Internet for their donations. Some 46 percent said that they expect to make a greater percentage of their charitable gifts online within the next five years.

• Fifty-six percent said that charities send too many e-mail messages, and 47 percent said they do not read as many messages from charities as they did in the past.

• Seventy-four percent said it's inappropriate for a charity to obtain their e-mail address from a commercial database, while 82 percent said they don't think it's right for charities to send them messages about another organization.

• Ninety-two percent of donors like getting year-end tax receipts by e-mail, while 83 percent want to get electronic updates on a charity's finances and spending. Seventy-four percent said e-mail messages are appropriate when notifying donors that it's time to renew an annual gift or to explain how a donation has been spent.

• Eighty-one percent of donors dislike messages that take an urgent tone in seeking a repeat donation.

• Forty-six percent of donors said the charity's messages do a good job of making them feel connected to the organization, while 43 percent said the messages are well written and inspiring.

Most of the donors want more say on the quantity of e-mail they receive from charities.