Noise/Grainy removal?

I'm new here, and I have a question

Sometimes when I lighten up a photo certain dark areas (not all and not all the time) get very grainy / noisy looking. Is there anyway to remove or compensate for that? Unfortunately, I was shooting in very low-light level conditions and I could not use a flash (shots of horses). I would like to be able to get clean 8x10 prints out of these, but the grain is so bad.

Thanks!

In the darker areas the camera has literally not picked up all the information there, so when you try to bring it out, it will bring out what it can but the info will be patchy which is why it looks grainy. You could perhaps try putting it through a noise reduction programme like Noise Ninja? I have come across this recently, I haven't had the chance to test it out yet, but they do a trial version where you can test it on your images first to see if it does what you want before you buy it

thanks! I will look into it. The Noise filter in PS does a decent job, except it really softens the focus. I'll definitely take a look at the Noise Ninja.