With the shock of the stock market collapse wearing off, investors are starting to get mad.

Lawyers who press investor complaints report an increase in telephone calls from clients who say that their brokers did them wrong. Other aggrieved investors are calling the arbitration services provided by the stock exchanges.

(In most cases you must arbitrate; your brokerage-account agreement prevents you from suing in court.)

You can't demand restitution for your own foolish decisions. But when brokers take advantage of your ignorance -- and you energetically pursue your case -- you do have a chance to collect. Lawyers identify two main sources of trouble today.

One is margin accounts that customers didn't realize they had.

When you buy stocks "on margin," you are borrowing up to 50 percent of the purchase price. If stock prices fall, you have to come up with more money or be sold out at a loss.

Yet thousands of customers say they didn't realize that they owned stocks on margin until their brokers called up and demanded more cash.

How can that happen? Easy.

Your broker might encourage you to borrow against the securities in your account to take a vacation or buy a car. The firm charges interest on the loan, which is "a huge source of revenue for the brokerage house," said Washington attorney Arthur Schwartzstein.

Your monthly statement may even highlight your "borrowing power" right at the top. Customers with cash-management accounts can write checks against them, or put down a credit card.

Because you are borrowing for some purpose other than owning more stock, you might not connect it with buying on margin. But it's all the same thing.

On Oct. 19, Black Monday, many margin customers weren't even given a chance to put up more money, according to New York attorney Mel Weiss.

Innocent investors might be able to contest their losses if they didn't realize they had margin accounts or if their broker didn't fully explain them.

The other thing that could cause trouble is speculative investments, pushed onto customers who didn't understand them.

In particular, Schwartzstein said, he's getting complaints about index options. "Their risks are often misrepresented," he says. "They're a lousy way to try to make a return."

Index options have been touted by some brokers as investments that could hardly go wrong. They advised you to sell "puts" on one of the stock indexes, usually the Standard & Poor's 100 index. Selling puts is a bet that stock prices won't fall.

As long as the market stayed flat or rose, speculators made money. Even if stocks fell, brokers said, they wouldn't fall far enough, long enough, to cause a big loss. Believing that, many innocents borrowed money to support their options habit.

Then came Black Monday. Speculators effectively wound up paying pre-Oct. 19 stock prices to cover their bets -- suffering losses far larger than the sums they had put up in the first place.

Unsophisticated investors, who obviously couldn't afford to gamble, are good candidates for recovering some of their losses.

Complaints about unanswered telephones and trading errors, the bane of the early days of the crash, are receding, according to St. Louis attorney Jay Sushelsky, a member of the arbitration panel for the New York Stock Exchange.

Sushelsky said every instance of faulty paperwork that came to his attention was corrected by the brokerage house -- even if the broker had to swallow a loss.

If you think he's wrong, don't scream to me. File an arbitration action and scream to him.

Unfortunately, there is no similar forum for complaints about financial planners, unless the planner is also a broker.

For information on how to pursue a complaint, write or call for the free booklet "Coping With The Crash, A Step-by-Step Guide to Investor Rights," prepared by the North American Securities Administrators Association, Suite 750, 555 New Jersey Ave. NW, Washington, D.C. 20001. The toll-free telephone number is (800) 942-9022.