An axe-murderer serving a life sentence for killing his wife is appealing a decision to deny him parole.

John Frederick Ericson killed his wife Sandra in 1999 by striking her in the back of the head with a tomahawk 22 times while she slept.

In its latest decision released in September last year, the Parole Board said it did not share Ericson's "optimism" about his readiness for release, and declined his parole.

The board said Ericson "seemed unwilling or unable to acknowledge the brutality of his actions" on the night of the "savage murder" 19 years ago.

"Nor could he respond to their concerns that he had never expressed remorse."

Ericson has taken his case to the High Court at Wellington today to challenge the board's decision.

It is not the first time he has taken court action - he has appealed board decisions numerous times in the past, and has yet to succeed in securing his freedom.

He has shown "marked changes in his behaviour and attitude" since his previous parole hearing, but the changes were too recent.

"He also needs to be exposed to a greater number of challenging situations and to demonstrate that he can deal with them appropriately," the board said.

In court today, Ericson's lawyer Michael Starling said the increase in the amount of time prisoners are spending before getting parole is important to consider.

"The Parole Board has never set out any policy or any detailed analysis of how they applied what seems to be a simple test that the person applying for parole doesn't pose an undue risk to the safety of the community," he said.

Justice Karen Clarke said in his statement of claim Ericson sought for her to order his release.

"I can't do that," she said.

Starling said what Justice Clarke could do was send the matter back to the Parole Board for reconsideration.

He said the importance and gravity of the board's decision needed to be looked at alongside "the complete lack of consistency and transparency in how they seem to be making decisions".

But Justice Clarke said there was no way to show there was inconsistency in the board's decisions without looking at "every single aspect" of a prisoner's history.

"There's no evidence even before the court of that in this case."

She said it was "an almost impossible undertaking given the individuality, the individualised decisions that are made in respect of each individual offender".

Starling referred to other Parole Board decisions where offenders had killed more people but got parole earlier.

One person he referred to was paroled six times and recalled six times, he said.

The offender was at "moderate risk of serious violent reoffending" but was still released on parole a number of times.

Justice Clarke questioned how looking at that offender's case helped Ericson with his claims of bias, unfairness, and unreasonableness against the board.

The hearing is expected to conclude today.