Great-West Life & Annuity Insurance Company has agreed to buy an 80% stake in Benefit Management Corp., the parent of Allegiance Benefit Plan Management Inc.

Great-West Life, Greenwood Village, Colo., is a unit of Great-West Lifeco Inc., Winnipeg, Manitoba, which, in turn, is a unit of Power Corp. of Canada, Montreal, a major financial services company.

Allegiance, Missoula, Mont., manages health coverage for Montana employers with 90,000 health plan members.

Great-West also will be acquiring control of the Allegiance physician and hospital network, a Benefit Management Corp. subsidiary that was created to sell fully insured health plans in Montana, and a company that provides medical management services, Great-West Lifeco says.

The shareholder who now owns Benefit Management Corp. will retain a 20% interest in the company, Great-West Lifeco says.

The Allegiance companies will keep their names and operate as subsidiaries of Great-West Life, with management and service staff remaining in place, Great-West Lifeco says.

Great-West Lifeco hopes to get the regulatory approvals it needs to complete the deal by June 30.