CTX is a three-letter abbreviation with multiple meanings:

• C-terminal telopeptide, a blood serum biomarker that can be measured to assess bone turnover
• Ceftriaxone, an antibiotic
• Cefotaxime, an antibiotic
• Cerebrotendineous xanthomatosis, a genetic disorder
• Charybdotoxin, a toxin found in scorpion venom
• Chemotherapy, treatment of cancer with cytotoxic drugs
• Cholera toxin, a toxin responsible for the harmful effects of cholera
• Ciguatoxin, a neurotoxin produced by marine dinoflagellates
• Conotoxin, a toxin found in cone snail venom
• Crotoxin, toxic compound in snake venom
• Cyclophosphamide, an anticancer drug

• Centrex, a telephone service
• Citrix Systems, company best known for desktop virtualization software
• Chuntex Electronic, computer display manufacturer based in Taiwan
• CTX (camera), on the Mars Reconnaissance Orbiter
• CTX (computer virus)
• CTX (explosive-detection device)
• Collisionless Terrella Experiment, a levitated dipole at Columbia University

• Caltex, where CTX is the stock symbol for Caltex Australia Limited

• Concordia University Texas, where 'C' is for Concordia and 'TX' is for Texas
• Countdown to Extinction, a thrill ride at Disney's Animal Kingdom, now known as DINOSAUR
• CTX, IATA airport code for the city of Cortland, New York, U.S.A.