In court today, the lawyers and their respective scientists battled over the statistical significance of the blood mixtures found in Mr. Simpson's Ford Bronco and on the gloves, and about how that evidence should be presented to the jury.

The debate centered on whether Dr. Bruce Weir, a professor of statistics and genetics at North Carolina State University in Raleigh, should be allowed to testify. Dr. Weir, a prosecution witness, has calculated that the combination of blood types found on the items would be relatively rare. Defense lawyers said they were much more common and tried to keep him from taking the stand.

The debate left minds wandering and eyes glazed, and after the lawyers spent several hours reviewing the professor's methodology, Judge Ito ruled that the professor could testify. Dr. Weir then began all over again, this time before the jury.

Dr. Weir testified how he had calculated the chances that any two people or any three people in the country could have contributed to blood mixtures on the bottom of Mr. Goldman's shoe. He said there was a range of 1 in 300 million to 1 in 1 trillion, a figure he said could be likened only to the national debt, that two randomly selected people could have had the same blood mixture found on the shoe.

Throughout much of this tedious day, Mr. Goldman's stepmother and sister, who have rarely been absent, were gone. So, too, were most of the principal lawyers, including Mr. Cochran, Mr. Darden, Robert L. Shapiro, a defense lawyer, and Marcia Clark, a prosecutor; members of Mr. Simpson's family, and Mr. Simpson himself, for a time. His lawyers say he was talking to them.

Juditha Brown, Mrs. Simpson's mother, was on hand as part of what family members say is their vow to maintain a constant presence in the courtroom.

In another development, prosecutors asked Judge Ito to bar Mr. Simpson's lawyers from calling Thano Peratis, the nurse who drew blood from Mr. Simpson the day after the killings.

At the preliminary hearing last year, Mr. Peratis estimated that he had drawn eight milliliters of blood from Mr. Simpson. Because the blood that can be accounted for is less than that amount, defense lawyers maintain that some of Mr. Simpson's blood is unaccounted for and that the police may have been sprinkling the missing increment on various items in an effort to frame him.