Key Points:

Tainui and Ngai Tahu's investment companies have banded together to buy a 6 per cent stake in retirement village operator Ryman Healthcare in the first joint purchase by the two iwi since signing a co-investment agreement at the end of last year.

Yesterday, Ngai Tahu Holdings Group bought 30 million shares from Australian investment company Babcock and Brown and then on-sold 22.5 million or a 4.5 per cent stake for $37.125 million to Tainui.

The purchase sees Ngai Tahu's holding increase from 6.5 per cent to 8 per cent while Tainui's 4.5 per cent stake is its first direct investment in the New Zealand sharemarket.

Tainui Group Holdings chief executive Mike Pohio said the two tribes signed a co-investment agreement in December to take advantage of any opportunities that would provide mutual advantages.

Pohio said the Ryman purchase was the first of its joint moves and there were plans for more further down the track depending on the opportunities presented.

"We have been co-operating on our respective fishing investments for some time, but this investment takes the relationship to a new level."

Pohio said Tainui wanted to diversify outside its mainly property assets and the Ryman stake presented a good chance to do that.

He said the investment company already had some of its money in shares through fund managers but the current market presented a good opportunity to invest directly.

"We have over $400 million in assets and only $30 million in debts and we are looking to leverage on that balance sheet."

In July Tainui bought the Warehouse's 50 per cent stake in Hamilton retail centre The Base for $37 million.