Background: Injection with botulinum A exotoxin reconstituted with preserved saline has been shown to be less uncomfortable than injection with the same toxin reconstituted with preservative-free saline. Objective: We sought to determine whether injection with botulinum toxin type B is similarly less painful when preservative-containing saline is used to further dilute the product. Methods: We conducted a double-blind, randomized controlled trial. A total of 15 consecutive adult patients presenting for treatment of upper face dynamic lines received treatment to one side (left or right) of the face with toxin type B further diluted with preservative-containing saline, and to the other side with toxin type B further diluted with preservative-free saline. Results: Of 15 patients, 13 (87%) reported less pain in the halves of their faces treated with the preservative-containing saline (P = .0006). Pain on the preservative-containing side was on average 32% less among patients as a whole, and 39% less among patients noting some reduction. The 95% confidence interval for pain reduction associated with preservative-containing injection was −46.9% to −16.1%. Neither investigators nor patients observed any difference in clinical efficacy between the 2 treatment sides. Conclusions: Use of preservative-containing saline to further dilute botulinum toxin type B can significantly decrease patient discomfort on injection. (J Am Acad Dermatol 2003;48:875-7.)