Nanomaterials are used in a broad range of consumer products, but their unique properties make them challenging to test in both in vivo and in vitro toxicity assays. ICCVAM established its Nanomaterials Workgroup to evaluate the suitability of alternative methods to assess potential toxicity of nanomaterials. The workgroup is sponsored by CPSC and NIST, and has members from seven ICCVAM agencies. The workgroup has surveyed federal agencies to determine needs and activities relevant to nanomaterials testing, potential applicability of alternative methods to testing needs, and the challenges that would be faced in implementing them. Its findings will be reported in a paper planned for publication in 2020.