This guidance provides information on one use by the Food and Drug Administration (FDA) of its authority to impose a clinical hold on a study or study site if FDA finds that human subjects are or would be exposed to an unreasonable and significant risk of illness or injury. Specifically, this guidance describes circumstances in which FDA may impose a clinical hold based on credible evidence that a clinical investigator conducting the study has committed serious violations of FDA regulations on clinical trials of human drugs and biologics, including 21 CFR Parts 312, 50, and 56, or has submitted false information to FDA or the sponsor in any required report. FDA may consider imposing a clinical hold in these situations where necessary to protect human subjects in the study from an unreasonable and significant risk of illness or injury. Such a clinical hold may be imposed on the study in which the misconduct occurred or on other studies of drugs or biological products in which the clinical investigator is directly involved or proposed to be involved. Although FDA has authority to take various enforcement actions against a clinical investigator who commits serious violations of FDA regulations, these actions may not be completed swiftly enough to protect human subjects who may be at risk in ongoing studies conducted by the investigator. Where the investigator's misconduct appears to pose an ongoing threat to the safety and welfare of such subjects, imposition of a full or partial clinical hold on ongoing or proposed studies of human drugs or biological products may be appropriate. See 21 CFR 312.42(b)(1)(i), 312.42(b)(2)(i), 312.42(b)(3)(iii), and 312.42(b)(4)(i). This guidance does not address other circumstances in which FDA may impose a clinical hold if FDA finds that human subjects are or would be exposed to an unreasonable and significant risk of illness or injury, including when there is no evidence of clinical investigator misconduct or a serious regulatory violation. This guidance finalizes the draft guidance of the same title dated April 2002.