Despite poor-quality toxicity tests, acesulfame potassium was approved by the US Food and Drug Administration (FDA) for use as an artificial sweetener. At present, acesulfame is very widely used, most frequently in blends with the most popular artificial sweetener in the US, sucralose (Splenda). Acesulfame was nominated twice (in 1996 and again in 2006) for testing in the National Toxicology Program (NTP) bioassay program. Both nominations were rejected by NTP. Rather than carry out bioassays, NTP subjected acesulfame to tests in genetically modified mice (GMM). Those GMM tests yielded results that provided no insight into potential carcinogenicity of acesulfame. It is possible that FDA discouraged NTP from conducting bioassays of acesulfame. Acesulfame should be tested in the bioassay program as soon as possible, and steps should be taken to ensure the objectivity of the bioassay nomination process.