The 2010 401(k) plan contribution limits are unchanged from 2009:
2010 401(k) Contribution Limits
The 2010 401(k) contribution limit remains $16,500. If you reached age 50 by December 31, 2010, then you can contribute an additional $5,500, for a total contribution of $22,000. That amount is also unchanged from 2009. (For the year 2008, the base contribution limit was $15,500 with a possible $5,000 catch-up contribution, so the potential total contribution for someone 50 or older was $20,500.) Make sure to check out this year's updates by reviewing the 2011 401(k) Contribution Limits.
Your employer’s restrictions may cause your individual contribution limit to be somewhat lower. Possible causes include a cap on the percentage of pay you are eligible to contribute and your employer not yet allowing for catch-up contributions.