Leidos Inc., Reston, Virginia, is issued a modification (P00029) to exercise Option Period Four with a ceiling value of $32,101,802 for a time-and-materials contract (HDTRA1-17-C-0019) for scientific and technical services in support of various projects under the Biological Threat Reduction Program. Work will be performed at various locations throughout the world. The anticipated completion date for Option Period Four is May 13, 2022. The contract was a competitive acquisition; the government received 11 offers. The Defense Threat Reduction Agency, Cooperative Threat Reduction Contracting Office, Fort Belvoir, Virginia, is the contracting activity.