You can use a slicker or mats brush/comb. I've found that usually you have to cut mats out. Prevention is the best method for dealing with mats. A daily brushing (or every other day) works wonders.

How long is the hair? Do you have a long haired breed, like an angora? They do require almost constant grooming. YOu need a really good mat rake. A good mat rake to try is the E-jay Rakom R-2, which can be ordered through your veterinarian, or simply a metal comb, preferably one where the teeth spin (the spinning teeth go through tangles easier). A slicker brush is not recommended because the bristles are sharp and too rough on the skin. In addition, slicker brushes only go through the top layer of fur, which doesn't mat. They are useless on long hair. For a rabbit that is severely matted, it is recommended that a rabbit savvy veterinarian or a professional groomer with rabbit experience shave the rabbit, or at least the very matted parts. A #40 blade is preferred, as rabbit fur is very fine and easily clogs up the clippers and blade. After being shaved, fur should then be groomed regularly to prevent further matting. Depending upon the severity of the mats, the shaving process may take several hours and the rabbit may need to be sedated to minimize stress. If you do not choose to have the matted parts shaved, it is recommended that you work on one section per day, being cautious not to stress or tire the rabbit. Take your fingers and gently pull the mats apart or snip into them with sharp, blunt scissors while holding your fingers between the bottom of the mat and the rabbit's skin to avoid cutting into the skin. As you pull or cut the mats apart, gently comb through the mat with a metal comb to remove lose fur. IMPORTANT: Do not pull the mat up when cutting into it! Pulling on the mat also pulls the skin up, making it easy to cut into the skin with your scissors.

thank-you all very much, you have been a big help to me.

The vets told me if you leave a rabbit with matted fur, during the summer period, often mites will breed in the fur and eat away at the rabbits skin so it is important that you dont leave it matted. Regards