Empirical data regarding payments to participants in research is limited. This lack of information constrains our understanding of the effectiveness of payments to achieve scientific goals with respect to recruitment, retention, and inclusion. We conducted a content analysis of consent forms and protocols available on clinicaltrials.gov to determine what information researchers provide regarding payment. We extracted data from HIV (n = 101) and NIMH-funded studies (n = 65) listed on clinicaltrials.gov that had publicly posted a consent form. Using a manifest content analysis approach, we then coded the language regarding payment from the consent document and, where available, protocol for purpose and method of the payment. Although not part of our original planned analysis, the tax-related information that emerged from our content analysis of the consent form language provided additional insights into researcher payment practices. Accordingly, we also recorded whether the payment section mentioned social security numbers (or other tax identification number) in connection with payments and whether it made any statements regarding the Internal Revenue Service or the tax status of payments. We found studies commonly offered payment, but did not distinguish between the purposes for which payment may be offered (i.e., compensation, reimbursement, incentive, or appreciation). We also found studies that excluded some participants from receiving payment or treated them differently from other participants in the study. Differential treatment was typically linked to US tax laws and other legal requirements. A number of US studies also discussed the need to collect Social Security numbers and income reporting based on US tax laws. Collectively, these practices disadvantage some participants and may interfere with efforts to conduct more inclusive research.