A Biosafety Level 4 laboratory (BSL4) is a type of research facility constructed to handle and contain the most threatening types of infectious organisms on earth. BSL4s work with biological materials that have been determined by the Centers for Disease Control and Prevention to represent the greatest hazards to human health. Although there are currently no BSL4s in Davis, UC Davis attempted to acquire the federal funding to create one in 2003. It would have been the only such lab on the entire West Coast. However, as one might expect, the NIMBY (Not In My Backyard) segment of the Davis population was dead set against this plan. One incident that greatly increased NIMBY sentiment was the 2003 escape of a monkey from the California National Primate Research Center at UC Davis; concerns arose that UC Davis might not be able to properly handle dangers of the magnitude associated with BSL4s if it was already having trouble maintaining labs that posed less risk.

Biosafety Level 3 labs are the next step down in terms of danger, but there are several of these that exist on the UC Davis campus.