U4

U4, U-4, or U04 may refer to:

Science and technology

 * U4 spliceosomal RNA, a non-coding RNA component of the major U2-dependent spliceosome
 * Haplogroup U4 (mtDNA), a human genetic group
 * U4, unitary group of degree 4
 * U-47700, a synthetic opioid
 * U04, the ICD-10 code for severe acute respiratory syndrome

Transport

 * U-Bahn lines
 * U4 (Berlin U-Bahn)
 * U4 (Frankfurt U-Bahn)
 * U4 (Hamburg U-Bahn)
 * U4 (Munich U-Bahn)
 * U4 (Vienna U-Bahn)
 * German submarine U-4, one of several German submarines
 * London Buses route U4
 * U-4, the U.S. Air Force version of the Aero Commander (aircraft), a light twin-engined aircraft from Aero Design and Engineering Company
 * U-4, the Japanese air self-defense force designation for the Gulfstream IV aircraft
 * U4, PMTair (former) IATA airline designator
 * U4, Buddha Air current IATA airline designator

Other uses

 * U4, the former name of the Maple League of Universities
 * U4, an unemployment figure released by the United States Bureau of Labor Statistics
 * Ultima IV: Quest of the Avatar, a video game