Used needles, and anything else contaminated and not scheduled for autoclave sterilization should be placed in these containers and removed in a timely manner.
For more information:
Sharps Waste ManagementInformation and photo examples of different types of sharps containers and how they should be disposed of.
Biohazardous Waste Description of what qualifies as biohazardous waste, and how it should be safely and effectively removed.
http://tattoo.about.com/cs/beginners/a/blsharps.htm