Although local steroid injection into the tenosynovium is a frequent treatment for carpal tunnel syndrome, it involves some risk and is not always effective. We simulated injection on 16 fresh cadaver forearms, instilling 1 ml (group 1) or 2 ml (group 2) of methylene blue at 1 cm or 3 cm proximal to the most distal wrist crease. Passive flexion and extension were simulated 2 minutes after injection by application of traction to the appropriate digital tendons. Specimens were dissected under loupe magnification from midpalm to midforearm, dye diffusion was quantified and photographed, sections of the carpal tunnel and contents were graded for presence of dye, and average values were determined for each of the four groups. Diffusion of dye was best in group 2B in which 2 ml was injected 3 cm proximal to the distal wrist flexion crease.