ATLANTIC CITY, March 31

Merck & Company asked for a mistrial Friday in the case of two men who blame Vioxx, the company's once-popular painkiller, for their heart attacks.

In its request, Merck said a plaintiff's lawyer, W. Mark Lanier, had tried to influence the jury by disclosing that his client had written letters to jurors thanking them for their service.

Merck also filed a motion for summary judgment, a common procedure in such cases, asking the judge to declare that the evidence was too weak for the jury to even consider the case.

The request for the mistrial came after Mr. Lanier told The Associated Press on Thursday that one plaintiff, Thomas Cona, 59, had written the letters to the eight jurors, to be given to them after the case ends. The letters were given to Judge Carol E. Higbee, who is presiding over the case in New Jersey Superior Court.

Judge Higbee has not decided whether to give them to the jurors, according to Theresa Ungaro, a spokeswoman for the judge.

Judge Higbee will hear arguments on each of the Merck motions on Monday, when closing arguments are scheduled in the four-week case.

In its defense, Merck said the plaintiffs, Mr. Cona and John McDarby, 77, had pre-existing conditions that were more likely the causes of their heart attacks and that Vioxx cannot be blamed.

Merck, based in Whitehouse Station, N.J., has won two cases and lost one in the legal fight over Vioxx, which was withdrawn from the market in 2004 after a study showed it doubled the risk of heart attacks and strokes after 18 months of use.

In the motion Friday, a Merck lawyer, Hope S. Freiwald called the letters an attempt by the plaintiffs ''to improperly influence the jury pool through extrajudicial comments.''

Telling jurors to disregard the statements would not fix the problem, and a mistrial is warranted, according to Merck's motion, which said the company's lawyer had not been told about the letters.

Mr. Lanier called the motion hypocritical, saying Merck was currently running TV commercials about itself in the Atlantic City market that could be construed as trying to sway jurors.

''Their motion is a diversion,'' Mr. Lanier said.