Examples
Worked examples
- Is an instance
A PI receives a two-year R21 to establish proof-of-concept for a new diagnostic assay; after meeting the milestones defined in the original R21/R33 application, the award transitions — without a new competing application — into a three-year R33 phase to validate the assay in a larger cohort.
- Is an instance
An IC's translational-research FOA uses the R61/R33 structure: the R61 phase supports early feasibility work with formal go/no-go milestones, and NIH program staff administratively review those milestones before releasing R33-phase funding for expanded development.
Counter-examples
Looks similar, but isn't
- Not an instance
A first-time investigator with no prior R21- or R61-phase progress applying to a general R33 funding opportunity that requires demonstrated R21-equivalent preliminary results — most R33 FOAs are not open to applicants lacking that foundation.
- Not an instance
Referring to an R33 as a 'cooperative agreement': R33 is an R-series NIH research grant, administered with standard investigator independence, not a U-series cooperative agreement carrying NIH's 'substantial programmatic involvement' obligations (e.g., U01).
Editorial commentary
An R33 is an NIH Exploratory/Developmental Grant Award that funds the second, expanded phase of a research project after early feasibility work has shown promise. R33 awards are most often used as the second half of a phased R21/R33 mechanism: the R21 phase funds early-stage, high-risk exploratory or developmental work over a short period (commonly up to two years), and progression into R33 funding is contingent on the grantee meeting specific, pre-defined milestones set out at the time of the original application.
How the R21/R33 phased award works
Because the R33 phase depends on milestones rather than a fresh, independently reviewed application, applicants typically submit a single application describing both phases up front, including the criteria NIH and the applicant agree will trigger the transition from R21 to R33 funding. The awarding Institute or Center reviews progress against those milestones administratively rather than through a new peer-review round before releasing R33-phase funding.
R33 vs. other NIH mechanisms
An R33 differs from a standalone R21 in that it presumes a longer overall project (the R21 phase alone typically cannot exceed two years, while R33 funding extends the total project further) and from an R01 in that R33 funding still targets development of a research direction toward eventual independent, hypothesis-driven investigation rather than funding that investigation directly. Not every Institute or Center participates in the R33 mechanism, and specific milestone and budget requirements vary by the funding opportunity announcement.
References
- NIH Grants & Funding, Types of Grant Programs — R33
- NIH Research Project Grant (R01) and Exploratory/Developmental (R21) mechanism descriptions
Frequently Asked Questions
What is an R33 grant?
An R33 is an NIH Exploratory/Developmental Grant Award that funds the second, expanded phase of a research project. It is most often awarded as the second half of the phased R21/R33 mechanism, once the applicant has met the specific milestones defined in the original application.
What is the difference between an R21 and an R33 grant?
An R21 funds early-stage, high-risk exploratory or developmental work, typically for up to two years, while an R33 funds a longer, expanded second phase that a project moves into only after meeting the pre-defined milestones set at the R21 stage. R33 is not a standalone award; it presumes a longer overall project than the R21 phase alone allows.
Do you need to submit a new application to move from R21 to R33 funding?
No. Applicants typically submit a single application describing both phases up front, including the milestones that trigger the shift from R21 to R33 funding. The awarding Institute or Center then reviews progress against those milestones administratively, rather than through a new peer-review round, before releasing R33-phase funding.
Is R33 funding guaranteed once you receive an R21 award?
No. Progression from the R21 to the R33 phase is contingent on meeting the specific, pre-defined milestones set out in the original application. If those milestones are not met, the project does not move into R33 funding.
How is an R33 different from an R01 grant?
An R33 still funds development of a research direction toward eventual independent, hypothesis-driven investigation, whereas an R01 funds that hypothesis-driven research directly. R33 is a developmental step rather than the final independent research award.
Is R33 funding always paired with an R21 grant?
Not necessarily. R21/R33 is the most common pairing, but R33 funding can also follow an R61 first phase, which uses the same go/no-go, milestone-based structure to determine whether a project advances into the R33 phase.
Also known as
R33 grant · NIH R33 · Exploratory/Developmental Grant Phase II · R21/R33 · R61/R33
Machine-readable encodings
Use in your systems
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