Is sex in the mind or the body? That was the question in a Florida court Tuesday as the custody battle between a transsexual man and his wife of 10 years got under way.

Central to the case of Michael Kantaras — who was born in 1959 as Margo Kantaras but took hormones and had his breasts, uterus, and ovaries removed to become a man — is the notion that sexual identity is a mental, not a physical construct.

"Sex is between your ears, not between your legs," testified Walter Bockting, an expert on transsexualism, on Michael Kantaras' behalf.

Bockting, a clinical psychologist who says he has helped 150 "gender dysphoric" individuals switch genders, was the only witness to testify in the opening day of this precedent-setting custody battle.

Linda Kantaras

Kantaras' wife, Linda Kantaras, claims that because her husband was born as a woman, their 1989 marriage is void under a 1998 Florida law banning same-sex marriages.

Linda Kantaras, 33, brought to the marriage a 1-month-old son, Matthew, whom Michael Kantaras adopted that year. Then, in 1992, Linda gave birth to a daughter, Irina, using sperm from Michael's brother, Thomas.

It was Michael Kantaras, however, who in 1998 filed in Pasco County, Fla., for divorce and custody of the couple's two children, now ages 9 and 12, after allegedly becoming involved with another woman.

The bench trial, the first of its kind in Florida, will provide Circuit Court Judge Gerard O'Brien the opportunity to set precedent on a number of issues, beginning with an age-old question revisited: What makes a man a man?

Bockting testified that the right genetic code isn't the only factor.

The expert said how the process of gender reassignment can also turn women into men. Gender reassignment, he explained, consists of three steps, taking male hormones, living for a period of time in the masculine "gender role," and receiving surgery to alter the body to remove some or all of the external female sexual characteristics.

Some transsexuals must undergo such a transformation, Bockting said, to relieve the psychological afflictions caused by feeling assigned to the wrong gender.

"One of my patients actually tried to cut off his breasts, because that wasn't how he saw himself," he said. "That is the level of despair that some female-to-male-transsexuals experience."

In 1987, Michael Kantaras underwent reassignment surgery at a Galveston, Texas, clinic — a procedure that removed his breasts and sculpted a male chest, and that removed his uterus and ovaries. However, Kantaras never had a penis constructed, which Linda Kantaras claimed in court documents to be grounds for considering him to be female.

Bockting told the court that a complete surgical transformation, however, is expensive and unnecessary for the reassignment to be complete. According to the expert, less than 10 percent of female-to-male transsexuals undergo phalloplasty, a surgical procedure that uses skin grafts and fat transplants to construct a penis in the place of the clitoris.

O'Brien, who interjected often to question the expert, asked, "Do you believe that having a small penis or having no penis at all makes an individual less of a man?"

"No," Bockting said.

Karen Doering, the lawyer for Michael Kantaras, closed her examination of Bockting with a nod toward the effect this case could have on her client's psychological well-being.

"And what would be the psychological, social, physical response of a person who has ... completed the sex reassignment process ... to then be declared by the court to be the gender they were assigned at birth rather than the one that they received through reassignment?" she asked.

"Well, I think that would be devastating. It's really an invalidation of their whole being," Bockting answered.

During the bulk of her examination, Doering led the expert through questions emphasizing the mental part of one's sexual identity.

O'Brien, however, asked a number of questions about the physical side of identity, at one point going into a lengthy rhetorical excursion on the chromosomal underpinnings of gender.

During her cross-examination, Linda Kantaras' attorney, Claudia Jean Wheeler, alluded to the Kantaras' son, asking whether a child would have problems if "he finds out that his father used to be a woman and the socks that he used to put in his pants are there because his dad used to put socks in his pants?"

"The way in which this news is presented is at least as important if not more important than the nature of the news," Bockting replied.

Following Wheeler's cross, O'Brien posed one final question, asking the expert whether male bonding would be hampered if the father lacked a penis.

"That male bonding where a male and a boy are involved is very important," O'Brien said. "Can a male undergo reciprocal bonding with a male whom he understands was born a woman and still maintains some physical characteristics of a woman?"

"He might not have as big of a penis, but he is a man," Bockting replied.

Live coverage of the trial on Court TV will continue at 9 a.m. Wednesday.