Seniors: Even if you are satisfied with your Medicare prescription-drug plan for 2007, you need to do some research before re-enrolling.

With the sign-up for next year beginning Nov. 15, some of the most popular providers are significantly increasing premiums and charges for drugs. Also, many plans have dropped or plan to drop coverage for certain medications.

A study by Avalere Health, a research and advisory firm, found that Medicare beneficiaries in the most popular plans will see a 21% increase on average in their 2008 monthly premiums. Some of the biggest providers built market share with low rates and are now significantly increasing them.

WSJ.com Sunday editon provides information on Medicare prescription- drug plans.

Visit Medicare.gov for complete information.