The role of practice guidelines in malpractice litigation has been discussed in some theoretical detail. Little information is available, however, on how courts use guidelines or on the effort of state legislatures to explicitly link guideline compliance with malpractice defenses. We review all relevant case law and legislative enactments to shed light on the influence of medical malpractice on guidelines. We also use data from a nationwide survey of malpractice attorneys to supplement our legal analysis. Although guidelines are being used for both inculpatory and exculpatory purposes in common-law litigation (a two-way street), legislatures are interested in applying them only for exculpatory purposes (a one-way street).