Prosecutors in Oslo are questioning Anders Behring Breivik about his contacts with militant nationalists as they seek to prove his far-right European network does not exist.
Breivik, who killed 77 people last July, gave few details but told the prosecutor not to ridicule him.
"Anyone could do what I did," Breivik told the court.
The judge told him he had the right to remain silent but not answering questions could be held against him.
The court is seeking to establish whether he is sane and can be jailed.
Breivik said the far-right network, which he named as the Knights Templar, met in London to decide on its platform. However, he refused to say whether a decision was taken on using violence.
Earlier, prosecutor Svein Holden told him the purpose of the questioning was to shed doubt on the network's existence.
Breivik said he hoped she would "ridicule me less and stick to the events".
In other parts of his testimony, Breivik told the court:
- he and other militant nationalists were "selling dreams" to inspire others
- he met a Serb nationalist in Liberia in 2001 who was one of the founding members of the Knights Templar
- he met his English "mentor", whose codename he gave as Richard the Lionheart, in London
- his own codename was Sigurd, after a 12th Century Norwegian king
"Why are you smiling?" the prosecutor asked him.
"Because you're asking me questions you know I'm not going to answer," he replied.
The prosecution showed the court an excerpt from Breivik's 1,500-page manifesto.
He wrote that he underwent a "complete screening and background check" for the Knights Templar to ensure that he was of "the desired calibre".
He claimed the group was considering "several hundred" individuals throughout Europe for a training course.
'Ruined our lives'
Breivik's testimony, and that of his witnesses, is not being broadcast. His testimony is expected to last for five days.
Breivik killed 69 people at a Labour Party youth camp on Utoeya island, having first set off a bomb outside a government building in Oslo that killed eight people.
On Tuesday, Breivik delivered a statement in which he said he would do it all again and asked to be acquitted.
He said he had acted to defend Norway against immigration and multiculturalism.
The leader of a support group for survivors of the 22 July attacks and victims' families says Breivik will be judged as a mass murderer, not as a man with a political agenda.
"The focus from our point of view is that he is not tried for his political views; he is on trial because he killed people, killed youngsters on Utoeya and my colleagues in the government quarters and that is the main focus for us," said Trond Blattmann.
"He has killed 77 people, he tried to kill several more, and he has ruined our lives and that is what he stands trial for and that is what is most important for us."
The BBC's Steve Rosenberg, in Oslo, says a contradictory picture of Breivik is emerging - a man who hates Muslims, but admired Osama Bin Laden and al-Qaeda.
Our correspondent says Breivik sees himself as a great Crusader, when in fact he was a high school drop out, a failed businessman and an addict of computer war games.
Earlier, Breivik's lawyers warned that many Norwegians would find his comments upsetting.
- Dagestan Russia blasts: At least 12 dead in Makhachkala
- Tymoshenko: Germany keeps up pressure on Ukraine
- France election: Sarkozy and Hollande trade insults
- Tymoshenko case: Europe pressure on Ukraine intensifies
- France election: Hollande takes lead into second round
- France ex-President Chirac 'to vote for Hollande'
- Breivik takes stand in Norway massacre trial
- Doctors battle to save one-in-a-million baby who was born with SIX legs
- Norway puts Anders Behring Breivik on trial for murder
- German incest couple lose European Court case
- Uefa slams Ukraine 'bandits' for Euro 2012 hotel prices
- 'I fell to my knees when I saw her': Mother finds 'stillborn' baby ALIVE in morgue 12 hours after she was pronounced dead
- French WWII resistance hero Raymond Aubrac dies aged 97
- Norway's mass killer Breivik declared sane
- Britain's hardest-working father emigrates to Australia with his wife and 12 children because the future back home is too grim
- Tymoshenko rejects Ukraine murder link as 'absurd'
- Brussels transport paralysed after fatal assault
- US to ease sanctions against Burma
- Greek unrest after pensioner suicide beside parliament
- West African Ecowas leaders impose Mali sanctions
- Russian plane crash kills 31 in Siberia
- Eight dead in Poland bus crash
- Spanish workers hold general strike over labour reforms
- Riot report reveals '500,000 forgotten families'
- Syria unrest: Divided opposition seeks 'national pact'