Thirty patients with chronic pain due to osteoarthrosis (OA) of the knee were enrolled in a randomised double-blind cross-over trial of self-administered transcutaneous electrical nerve stimulation (TENS) and placebo TENS. Medication was standardised to paracetamol tablets only. As measured on visual analogue scales for pain relief 46% of patients responded to active therapy and 43% to placebo. The length of pain relief during active therapy was significantly longer than that during placebo. At the end of the trial more patients wanted to continue using active TENS in preference to placebo or their original medication. Although most of the parameters observed favoured active TENS, it was not possible to establish its clear superiority over placebo, because the response rate to placebo TENS was high and sustained for at least 3 weeks. This trial suggests that a longer study is required to establish the role of TENS as a therapeutic agent in the treatment of the pain of chronic arthritis.