Italian Severino Antinori and American Panayiotis Zavos told a symposium here that they were motivated solely by the desire to help infertile couples have children.
"Cloning may be considered as the last frontier to overcome male sterility and give the possibility to infertile males to pass on their genetic pattern," Antinori told scientists and journalists at the city´s Umberto I Polyclinic.
"Some people say we are going to clone the world, but this isn´t true," he said. "We´re talking science, we´re not here to create a fuss."
Antinori is no stranger to controversy. He attracted criticism when he helped a 62-year-old woman give birth.
Panos Zavos, who quit earlier this month from his post at the University of Kentucky after announcing he was going to work on the cloning project, said the researchers had been bombarded with e-mail from couples anxious to have children through the new technology.
"They come to us and they don´t call you names, they don´t cuss you, they don´t say you´re unethical," Zavos said. "They said, ´Help me.´ Dolly is here and we are next," Zavos said, referring to the sheep that became the first adult mammal clone in 1996.
The Vatican has spearheaded religious opposition to cloning as well as the manipulation of existing human embryos -- such as "spares" from in vitro fertilization treatment -- for research.
Scientists believe that stem cells can be used to treat degenerative diseases. Some argue that those harvested from embryos would offer better results, while others -- backed by pro-life groups -- say adult stem cells, taken for example from newborn babies´ umbilical cords and from placentas, offer an effective and ethical alternative.
Experts working with the animal clones doubt whether Zavos and Antinori can actually make the technology work in humans. "The probability is that it can be done, but it is not inevitable that it can be done," said Dr. Harry Griffin, of the Roslin Institute, the Scottish center where Dolly was produced.
"Certainly, the efficiency [of animal cloning] in published work is very low -- around 2% of the embryos that are created by cloning make it to term," Griffin said. "Critically for this debate, many of the animal clones die late in pregnancy or soon after birth and show developmental abnormalities."
At the Rome symposium, Antinori tried to downplay the dangers of cloning. "Cloning creates ordinary children," he said. "They will be unique individuals, not photocopies of individuals."
He did not indicate which of the couples that had volunteered would be chosen for the program, but said he had ruled out single women and couples who wanted to have another child after the death of other offspring.
He gave no indication when or where he might attempt cloning but said he had no intention of breaking any laws. Antinori told the BBC he had an invitation from an unnamed Mediterranean country to set up a cloning clinic.