The state's highest court Tuesday allowed a grand jury to keep investigating one of the few U.S. doctors who performs late-term abortions but limited its power to subpoena his patients' records.

The Supreme Court refused to strike down the law abortion opponents used to force Sedgwick County to convene the grand jury to investigate whether Dr. George Tiller violated state restrictions on abortion.

The high court also declined to quash subpoenas it issued to Tiller and Attorney General Steve Six.

But in its unanimous ruling, the Supreme Court said there are limits on the grand jury's power.

The justices set guidelines and ordered the presiding district court judge to follow the new standards in determining whether the subpoenas should be enforced.

"The court should satisfy itself that the grand jury has not engaged in an arbitrary fishing expedition and that the targets were not selected and subpoenas issued out of malice or with intent to harass," Justice Lee Johnson wrote for court. "If so, the court should quash the subpoenas."

The Supreme Court said the district court must determine whether the documents sought are relevant to the grand jury's investigation, whether its subpoenas are too broad and whether complying would create too great a burden for Tiller and his clinic. It also must determine whether the subpoenas represent harassment, the justices said.

After that, the Supreme Court said, the presiding judge must protect patients' privacy. Tiller's clinic must be allowed to edit out information identifying patients, and what the court receives can be shared only with the grand jury, the justices said.

Abortion opponents generally were pleased with the ruling, though some said they had to review the court's decision. Anti-abortion groups had feared that the Supreme Court would quash the subpoenas or even dissolve the grand jury.

A Six spokeswoman and attorneys for Tiller and a national group representing his patients praised the court for limiting the grand jury's power. They said the justices' rules should protect patient privacy.

The grand jury targeted records from about 2,000 Tiller patients, including women who had been to the clinic but not obtained abortions, though an attorney for the panel said it would settle for far fewer documents. The panel also sought the edited copies of 30 records obtained by the attorney general's office in a previous investigation.

The attorney general's office already has filed 19 misdemeanor charges against Tiller in Sedgwick County, alleging that the doctor failed to obtain a second opinion for some late-term procedures from an independent physician, as required by law. Many abortion opponents believe Six should be pursuing more serious charges, which is why they forced the grand jury to convene.

Kansas is one of six states that allows residents to petition to form grand juries, and the court ruled Tuesday that the practice was constitutional.

Tiller attorney Lee Thompson said that he still believes the grand jury law is unconstitutional, but he was pleased that the court set guidelines.

"It's a very good decision recognizing that the grand jury does not have unfettered powers and the grand jury subpoenas require a degree of judicial oversight," Thompson said.

Associated Press Writer Carl Manning also contributed to this report.

Copyright 2008 Associated Press