| B | Experiments which cause little or no discomfort or stress. |
| C | Experiments which cause minor stress or pain of short duration. |
| D | Experiments which cause moderate to severe distress or discomfort. |
| E | Experiments which cause severe pain near, at, or above the pain tolerance threshold of unanesthetized conscious animals. |
The CCAC requires institutional animal care committees (ACCs) to ensure that any potential pain and/or distress is minimized. Anesthetics and analgesics must be used; any exceptions require scientific justification and ACC approval.