Background: Progress in clinical trial research depends on effective recruitment to ensure adequate sample sizes and generalizability of results. Electronic health record (EHR)–based recruitment has been suggested as a potential method to address historical imbalances in trial populations, including underrepresentation of certain racial and ethnic groups. However, disparities in EHR portal uptake and use exist, particularly among these same underrepresented groups. Thus, we hypothesized that EHR-driven recruitment for research may continue to exacerbate these dynamics. Objective: In this study, we evaluated whether a financial incentive improved response rates to recruitment messages delivered through an EHR portal in an equitable fashion. Methods: A random sample of 1200 patients with diagnoses of breast, colorectal, prostate, or lung cancer and active EHR patient portal accounts received an automated recruitment message for a fictitious cross-sectional survey study, “The Social Aspects of Cancer Care,” via their EHR portal. Two strata of patients were sampled, those who identified as non-Hispanic White individuals (n=600, 50%) and those who identified as part of a historically underrepresented racial or ethnic group (n=600, 50%), and randomized to receive an offer of a US $20 monetary incentive (n=400, 33.3%) or no incentive (n=800, 66.7%). Patients were given 14 days to respond. Results: Overall, 39.3% (471/1200) of participants viewed the recruitment message, and 13.3% (159/1200) responded that they were interested. Response rates were higher (<.001 among non-hispanic white patients than african american or black and members of other racial ethnic groups older years were less likely to view the recruitment message vs respond sex was not significantly associated with viewing response outcomes respectively no differences observed in rate for incentive cohort compared conclusions: cancer who identify as part a historically underrepresented group messages research studies through their ehr patient portal. age also found impact engagement respond. finally modest us financial engagement.>