805 ILCS 10/11
No corporation organized under this Act may issue any of its capital stock to anyone other than an individual who is duly licensed or otherwise legally authorized to render the same specific professional services or related professional services as those for which the corporation was organized. No shareholder shall enter into a voting trust agreement or any other type of agreement vesting another person with the authority to exercise the voting power of any of his stock.
The articles of incorporation shall provide for the purchase or redemption of the shares of any shareholder upon his death or disqualification, or the same may be provided for in the by-laws of the corporation or in a separate agreement of the interested parties.
If the articles of incorporation, by-laws or separate agreement fail to state a price or method of determining a fixed price at which the corporation or its shareholders may purchase the shares of a deceased shareholder, or a shareholder no longer qualified to own shares in the corporation, then the price for such shares shall be the book value as of the end of the month immediately preceding the death or disqualification of the shareholder. Book value shall be determined from the books and records of the corporation in accordance with the accounting methods used by the corporation.
805 ILCS 10/11