Forty-six patients with herpes zoster were randomised into two groups treated with DMSO alone and 5 percent IDU in DMSO, provided that treatment started within 48 hours of the appearance of a rash. In the IDU group the interval before pain improved was significantly shorter than in the control DMSO group, and significantly fewer new vesicles developed at the three day follow up in the active group compared with the control group. These findings are in agreement with previously published work and confirm the usefulness of Zostrum (5 percent IDU in DMSO) in the treatment of herpes zoster.