PURPOSE: To evaluate the timing of improvement after extra-articular steroid injection, the incidence of a postinjection pain flare (a delayed postinjection transient increase in pain), and the role of the injection acidity in the postinjection flare. METHODS: One hundred twenty-five patients with trigger finger (88 patients) or de Quervain's tenosynovitis (37 patients) were prospectively randomized in this double-blind study to receive either an injection of steroid, lidocaine, and bupivacaine alone (standard injection, acidic pH) or an injection of steroid, lidocaine, bupivacaine, and bicarbonate (balanced injection, neutral pH). All patients completed a visual analog scale for pain before and immediately after the injection, daily for 7 days, and then again at 6 weeks. A flare reaction was defined as an increase in the visual analog scale score by 2 or more points any time after the injection. RESULTS: All patients immediately responded to the steroid injection, but pain rebounded to preinjection levels by day 1. In both groups the pain then gradually declined over the course of 7 days. In the balanced group, 23 of the 68 patients had flare reactions. In the standard group, 18 of the 57 patients had flare reactions. The difference between groups was not significant. CONCLUSIONS: Patients respond to extra-articular steroid injections with gradual improvement over the course of the first week. An increase in pain, or flare reaction, in the days following a steroid injection was noted in 33% of patients. A pH-balanced injection did not significantly decrease the risk of a flare reaction. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic I.