In order to analyze the pressure on the carpal tunnel in the acute phase after Colles' fractures 13 patients were studied. The initial pressure and the variation after injection of a local anesthetic into the fracture hematoma, as well as the effects of increased volar flexion of the wrist, were measured using a wick catheter technique. Comparisons were made with a control group of ten healthy volunteers. The pressure was significantly higher in the fracture group than in the control group, and it increased significantly after injection of a local anesthetic into the fracture hematoma. A correlation was found between high increases after local anesthetic injection and high initial pressure. The pressure increased linearly with volar flexion of the wrist. There was a correlation between high increases due to volar flexion of the wrist and high initial pressure. The trauma itself causes increased carpal tunnel pressure due to edema and bleeding. Injection of a local anesthetic solution increases the fluid content of the carpal tunnel and raises the pressure. Volar flexion of the wrist decreases the space in the carpal tunnel, which also increases the pressure.