In acute whiplash injuries, early physiotherapy has been shown to reduce pain and increase cervical movement, but the cost-effectiveness of this treatment has been questioned. It is unclear whether the benefits result from manipulative physiotherapy or from the patient's ability to perform the accompanying home exercise programme when instructed about its importance. In a single blind prospective randomized trial 71 patients who received out-patient physiotherapy were shown to have significant improvement in severity of neck pain (P less than 0.01) and cervical movement (P less than 0.01) at 1 and 2 months post-injury when compared with 33 patients who received analgesia and a cervical collar. Sixty-six patients who were offered comprehensive advice for home mobilization by a physiotherapist showed a similar improvement. There appears to be no difference in effectiveness between outpatient physiotherapy and home mobilization.