AUSTRALIA'S only listed health insurer, NIB Holdings, has formed an alliance with the National Australia Bank that it hopes will boost its membership base by 5000 by the middle of next year.

The Newcastle-based insurer said the deal with the NAB, which will allow it to market its products directly to the bank's customers and offer them a "value health insurance" product, is an early step into the financial services sector.

"We've made no secret of the fact that we're very interested in developing growth and diversification opportunities, particularly in the financial sector," the managing director of NIB, Mark Fitzgibbon, said.

He said NIB saw the deal as a significant step towards realising these ambitions.

The sharemarket responded positively to the news, pushing up the NIB share price by 6c to 87c, and the NAB share price by $1.12 to $21.44.

Despite saying it expected to add 5000 customers over the next 15 months by tapping into NAB's customer base, the insurer has not altered its guidance for this financial year, and has declined to issue guidance for the 2010 financial year. For this financial year, the insurer expects its policyholder numbers and net underwriting margin to grow by about 4 per cent.

John Salamito, the regional general manager for NAB's consumer product solutions, said the bank looked forward to diversifying its services.

"We have teamed up with NIB to add a range of health insurance products to expand our current financial and non-financial suite of products that will continue to provide real value to our customers," he said.