This article first examines the nature of the seizure and the search that occur when the government demands an employee urine sample for chemical testing. This is followed by an assessment of government interests asserted to justify employee drug testing. These interests are critical issues in the fourth amendment's 'reasonableness' test. The article reviews exceptions to a search warrant supported by probable cause, since some exception must underlie employee drug testing as currently used or contemplated by public employers. Fourth-amendment ground rules are then applied to determine whether without-cause drug testing and drug testing based on 'reasonable suspicion' are constitutional. The article concludes that no exception to the search-warrant and probable-cause requirements should be created to countenance wide scale drug testing. Without-cause testing is clearly unconstitutional, and the reasonable-suspicion standard is insufficient rationale for the serious threat to personal privacy posed by the government's seizure and chemical evaluation of a person's body fluids. In exploring possible extensions of the constitutional analysis to drug testing by private employers, the article focuses on Massachusetts law, which contains at least three potential bases for challenging drug testing in the private sector: the State civil rights act, the invasion-of-privacy statute, and the common-law covenant of good faith and fair dealing. 235 footnotes.