Mitsubishi Chemical Corp., the nation's largest comprehensive chemical firm, and Tokyo Tanabe Co., a medium-size medicine maker, announced Thursday they will merge Oct. 1, a development that could trigger a realignment of the nation's pharmaceutical industry.

The deal, which will create a company with projected annual sales of 90 billion yen, has been approved by the two companies' boards. The new company formed by the merger will set up a wholly owned subsidiary to take over Mitsubishi Chemical's drug manufacturing section as well as Tokyo Tanabe's business rights, operations and employees, the companies said.

They said the deal benefits Mitsubishi Chemical by giving it a direct sales force for its drug business, on which it currently spends an estimated 14 billion yen a year for research and development.