Note 8 - Income Taxes

3 Months Ended

Mar. 31, 2016

Notes to Financial Statements

Income Tax Disclosure [Text Block]

8.     Income Taxes

Because of our historically significant net operating losses, we have not paid income taxes since inception. We maintain deferred tax assets that reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. These deferred tax assets are comprised primarily of net operating loss carryforwards and also include amounts relating to nonqualified stock options and research and development credits. The net deferred tax asset has been fully offset by a valuation allowance because of the uncertainty of our future profitability and our ability to utilize the deferred tax assets. Utilization of operating losses and credits will be subject to substantial annual limitations due to ownership change provisions of Section 382 of the Internal Revenue Code. The annual limitation will result in the expiration of net operating losses and credits before utilization.