The topic of nonprofit commercialization has received increased attention from various groups including donors, regulators, and researchers. Perhaps the most commercial of all activities undertaken by nonprofits are those considered to be so far removed from an organization's exempt mission that the Internal Revenue Services (IRS) considers them to be taxable. Examination of these taxable activities can provide unique and valuable insights into the effects of purely commercial activities on nonprofit behavior. Nonprofits report their taxable activities on the confidential IRS 990-T. Although some information on taxable activities is reported on the publicly available IRS 990, unavailability of the IRS 990-T has prevented prior examination of its accuracy and reliability. Using a unique data set of otherwise confidential IRS 990-Ts, the authors calibrate the reliability of taxable activities as reported on the IRS 990, providing a roadmap for researchers to follow when examining nonprofits' taxable activities using publicly available data.