A discussion of State statutes and proposed Federal legislation authorizing an exception to the rule of confidentiality is followed by an assessment of the potential effects of these laws on the therapeutic relationship and therapists' authority to warn third parties. The article also considers reasons not to impose such a duty. Alternative approaches are applied first to spouses, then to sexual partners or intravenous needle-sharing partners who are identifiable and limited in number. The article explores the desirability of providing therapists and counselors with discretionary authority to warn spouses or sexual partners rather than fixing mandatory duty to warn. The article concludes that the warning of third parties is most likely to be therapeutic by including the patient in the discussion with the third party, especially if there will be continuing contact between the patient and the third party. 121 footnotes.