Abstract: A lockout for use with a fluid injection valve which injects fluids in a tubing string of a well. The lockout, when actuated, holds the injection valve open for allowing passage of well tools therethrough; but when deactuated, allows the injection valve to operate normally. In combination with a spring-loaded, normally closed injection valve, which is opened by pressure actuating a flow tube in response to injection flow, of a lockout having a second flow tube coaxially aligned with the first flow tube for engagement therewith, piston means connected to the second flow tube and adapted to be actuated by fluid pressure from the well surface for moving the second flow tube against the first flow tube for holding the injection valve open, and a biasing spring acting against the second flow tube for moving the second flow tube away from the first flow tube whereby the injection valve may operate normally and independently of the lockout.