According to the latest U.S. Department of Agriculture statistics, about 8% of the regulated animals used in research experience pain or distress that's not alleviated by painkillers, and, as a result, they are placed in Category E on the annual reports submitted by institutions. (Category C is for animals that experience no or only momentary pain and distress, while Category D is for animals that receive drugs to alleviate some or all of the pain and distress they might experience.) There is tremendous variation in the way different institutions report their use of animals by pain category. Wide variation is also evident in state-by-state reports. In 1992, a reported 5.6% of laboratory animals were used in projects in which they experienced pain and distress. However, Kansas (45.5%), Washington (30.4%) and Colorado (26.0%) reported that at least a quarter of their animal research involved unrelieved pain, while some relatively big users like Arkansas (0.0%), Delaware (0.7%), Florida (0.7%), Maryland (0.8%), Massachusetts (1.0%), Nebraska (0.1%) and Texas (0.7%) reported less than 1% of animal research fell into the unrelieved pain category.

In Great Britain, the only statistical indication of pain control is the recording of anesthesia use. In 1978, 3% of the 5.2 million procedures involved anesthesia for the whole procedure (they were terminal), and 14% involved anesthesia for only part of the procedure. In 1988, 19% of the 3.5 million procedures involved anesthesia for the whole procedure, and 17% involved anesthesia for only part of the procedure. It is not clear why anesthesia use doubled from 1978 to 1988, although the 1986 act that revised British controls over animal experimentation placed greater emphasis on the control of pain and distress (The Alternatives Report, 1990).

The Netherlands has made a concerted attempt to classify its research animal use by pain category. Their 1990 annual report on animal experimentation notes that 53% of the animals experienced minor discomfort, 23% were likely to experience moderate discomfort, and 24% were likely to experience severe discomfort. About one fifth of the animals in this last category were given medication to alleviate pain. Examples of procedures that would place animals in the "severe" category are prolonged deprivation, experimental infections, tumor induction, toxicity testing and immunization protocols (The Alternatives Report, 1992).

The Swiss government classifies pain experienced by lab animals according to the degree of severity (i.e. "minimal to no pain"; "moderate pain"; and "severe pain"). The 1999 report showed 68% of research animals experienced minimal to no pain, 24.9% experienced moderate pain, and 7.1% experienced severe pain.

The problem of animal pain, distress and "suffering" in the laboratory is complicated. The HSUS has launched a campaign to clarify what we know about animal pain and distress, what types of procedures cause pain and distress, and how we may eliminate such pain and distress in the research laboratory by the year 2020.