"These are ill-willed fabrications," Breivik said, referring to passages from a court-ordered psychiatric evaluation that concluded late last year that he was suffering from paranoid schizophrenia.
He later added: "They may not be ill-willed, but they are in any case wrong."
Psychiatrists Synne Soerheim and Torgeir Husby were appointed by the Oslo district court to carry out a first evaluation of the 33-year-old right-wing extremist's mental health.
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Their conclusion in November that he was psychotic cleared the way for him to be sent to a closed psychiatric ward for treatment instead of prison.
Breivik wants to be found sane and accountable for his actions, so that his anti-Islam ideology will be taken seriously and not considered the ravings of a lunatic. He has already said that being sentenced to closed psychiatric care would be "worse than death".
The first diagnosis caused an uproar in Norway, where many were astounded that the man who methodically planned his attacks for years and then executed them with precision could be found not responsible for his actions.
The court therefore ordered a second opinion by two other experts, who concluded earlier this month that Breivik was sane.
It will ultimately be up to the panel of judges to determine whether he is sane when they hand down their verdict in July.
