NIH R21 Grant Requirements

NIH R21 clinical trials

The R21 grant mechanism is intended to encourage exploratory/developmental research by providing support for the early and conceptual stages of project development. The NIH has standardized the Exploratory/Developmental Grant (R21) application characteristics, requirements, preparation, and review procedures in order to accommodate investigator-initiated (unsolicited) grant applications.

This website describes the use of the R21 and describes the NIH Institutes and Centers (ICs) that intend to accept such applications.

Application Characteristics

  • You may request a project period of up to two years
  • The combined budget for direct costs for the two year project period may not exceed $275, 000. No more than $200, 000 may be requested in any single year.
  • The R21 can not be renewed
  • One resubmission (A1) is allowed
  • Introduction required for a resubmission is limited to one page.
  • No preliminary data are required but may be included if available.
  • The Research Strategy may not exceed 6 pages.


  • Exploratory, novel studies that break new ground or extend previous discoveries toward new directions or applications.
  • High risk high reward studies that may lead to a breakthrough in a particular area, or result in novel techniques, agents, methodologies, models or applications that will impact biomedical, behavioral, or clinical research.
  • Projects should be distinct from those supported through the traditional R01 mechanism.

All investigators should consult the list of participating ICs (shown below) as well as the to determine if an R21 application is appropriate. Investigators are strongly encouraged to consult with the appropriate NIH program administrator about their proposed research project during the concept development stage of the application.

All R21 grant applications will be assigned to the ICs according to standard PHS referral guidelines and specific program interests. Applications that are assigned to an IC that does not participate in this program may be returned without review.

There is also a list of ICs that do not accept unsolicited R21 applications. Non-participating ICs might solicit other R21 applications using Requests for Applications (RFAs) or Program Announcements (PAs) to meet specific program needs. Information about such initiatives can be obtained in the NIH Guide for Grants and Contracts and by consulting with NIH staff. In some cases those announcements may specify different application characteristics, review criteria, and receipt dates.

R21 Participating Institutes and Centers


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