CA4

CA4 may refer to:


 * Carbonic anhydrase 4, an enzyme that in humans is encoded by the CA4 gene
 * Cornu Ammonis region 4, a region of the hippocampus
 * United States Court of Appeals for the Fourth Circuit

CA-4 may refer to:
 * CAC CA-4, a 1941 Australian bomber aircraft
 * USS Pittsburgh (CA-4), a 1901 United States Navy armored cruiser
 * California's 4th congressional district
 * California State Route 4
 * Central America-4 Border Control Agreement, a boundary treaty between Guatemala, El Salvador, Honduras, and Nicaragua
 * Combretastatin A-4, a natural polyphenol

Ca4 may refer to:
 * Ca4 line, a regional Catalonia railway line connecting Barcelona and Lleida-Pirineus

Ca4 may refer to:
 * 4 atoms of Calcium

Ca.4 may refer to:
 * Caproni Ca.4, an Italian heavy bomber of the World War I era