SAN FRANCISCO -- The first week of the federal perjury trial of Barry Bonds wrapped up Thursday, with the fourth day devoted to defense cross-examination of government witness Steve Hoskins and questioning from both sides of Dr. Larry Bowers -- called by the prosecution as an expert on the side effects of steroid and human growth hormone use.

The trial, which will be conducted only Monday through Thursday each week, will resume Monday morning, with the government expected to call ex-mistress Kimberly Bell to the stand after current Internal Revenue Service agent Mike Wilson and former IRS agent Ana Geter testify.

Bonds, baseball's all-time home run leader, is charged with four counts of perjury and one count of obstruction of justice in relation to his testimony before the Bay Area Laboratory Co-Operative (BALCO) grand jury in December 2003, in which he denied knowingly using performance-enhancing substances.

Following the conclusion of the arduous testimony of Hoskins, Bonds' childhood friend and fellow business partner, Assistant U.S. District Attorney Jeffrey Nedrow called Bowers to the stand. The chief science officer for the U.S. Anti-Doping Agency, based in Colorado Springs, Colo., Bowers testified about different types of anabolic steroids, their effects and how they've come to be detected over the years.

Included in his testimony was the fact that his organization first came in contact with the "cleverly designed" drug THG -- or "the clear," as the once-undetectable steroid has become known through the investigation into BALCO that is at the root of this trial -- when a syringe with a small amount of it was sent to USADA in August or September 2003.

Bowers went on to detail different side effects steroid use can cause, and his testimony appeared to set up testimony from Bonds' former girlfriend. According to court documents, Bell is expected to testify that Bonds told her he took steroids and that she saw physical changes in Bonds, including bloating, acne on the shoulders and back, hair loss, sexual dysfunction and testicular shrinkage, along with so-called "'roid rage," or mood changes brought on by steroid use -- all side effects discussed by Bowers on the stand.

Bowers also testified that he believes use of human growth hormone can lead to a condition called acromegaly, symptoms of which include changes in hat, ring and shoe size -- side effects several witnesses are expected to testify they saw in Bonds.

Lead defense attorney Allen Ruby, who had grilled Hoskins for about four hours at the end of Wednesday and into Thursday morning's session, focused much of his time in cross-examination of Bowers on acromegaly and 'roid rage, using studies to suggest that there is very little information to connect those to use of performance-enhancing drugs.

In his questioning, Ruby depicted acromegaly as a degenerative disease that severely weakens those afflicted by it, obviously suggesting that Bonds as a world-class athlete did not suffer from it. Ruby also presented a study of steroid use that included 53 participants, 42 of whom had no episodes of violent behavior while the rest had only mild symptoms.

On Thursday morning, Ruby concluded what was a long, at times intense cross-examination of Hoskins, often referring to the April 26, 2005, meeting with government investigators. He also established through questioning that Hoskins paid for Bell's initial legal fees, and that Bell and Hoskins have had contact in recent weeks, although Hoskins denied that they discussed their upcoming testimony in the trial.

Ruby's questions and Hoskins' answers brought out inconsistencies between what Hoskins was reported to have said at that meeting in April 2005 and what he said on the stand. Ruby pointed out that Hoskins told investigators in that meeting that Bonds had not spoken to him about going to the authorities to report Hoskins' alleged business misconduct, but Hoskins admitted on the stand that Bonds and/or his business attorney, Laura Enos, had discussed it with him. Ruby also got Hoskins to amend what he'd told investigators about his sister's knowledge of Bonds' use of performance enhancers.

Asked Ruby: "You told them your sister, Kathy Hoskins, had told you that she saw [trainer Greg] Anderson 'shoot up' Barry before probably every road trip in 2002. Is that what you said?"

Upon reflection, Hoskins said, "She didn't tell me how many. She just said she had seen injections before road trips."

Hoskins also said that he talked to Dr. Art Ting, Bonds' surgeon, about Bonds and steroids, "Probably 50 times, maybe." Also, Hoskins testified that Ting told him that Bonds' elbow injury that required surgery in 1999 was due to steroid use.

Much like the testimony of Hoskins, Bell's testimony is expected to draw intense cross-examination from the defense. The two IRS agents who precede Bell on the stand will be there to testify as to transporting Bonds' urine specimens, seized via a search warrant in 2004, from Quest Diagnostics in Las Vegas to the UCLA Analytical Lab.

Former Giants trainer Stan Conte, now with the Dodgers, and Kathy Hoskins, Bonds' former assistant and sister to Steve Hoskins, also are expected to testify as the prosecution's case goes into its second week.