A witness reported that Gerald Mitchell (defendant) was driving drunk to police. Officers found Mitchell slurring and stumbling. A portable breathalyzer registered his blood-alcohol content (BAC) at triple the legal limit. Police transported Mitchell to the station to administer an evidence-grade breathalyzer, but Mitchell had become too lethargic. Officers transported Mitchell to the hospital, but he passed out on the way. An officer read Mitchell the standard prefatory statement required before administering blood tests in Wisconsin, heard no reply, and directed hospital staff to draw a blood sample. The test showed that Mitchell’s blood-alcohol level remained almost triple the legal limit 90 minutes after his arrest. The trial court admitted the blood-test evidence over Mitchell’s objection, and the jury convicted him. Mitchell appealed on the ground that the blood test constituted an unreasonable search without a warrant in violation of the Fourth Amendment. The Wisconsin Supreme Court affirmed his conviction, but the United States Supreme Court granted review.