A computer program is traced by associating a trigger with at least one code location, and upon encountering the trigger during execution, selectively enabling trace data collection data at subsequent traceable events. Preferably, collection of trace data is enabled only for procedure instances active (i.e., currently executing or on the call stack) at the time that the trigger is encountered. Preferably, a special environmental flag is set on encountering the trigger, saved in each current stack frame, reset on calling any new procedure, and restored from the stack on return from a procedure. Collection of trace data on a traceable event (such as an explicit trace statement in the code) is conditioned on the state of the special environmental flag.