Thirty-nine patients with cold urticaria seen over a 12-year-period were re-examined. All but 12 still had positive skin tests for cold and only five of these had shown a spontaneous cure. Fourteen patients were prone to collapse on cold exposure. The incidence of atopy in this group was comparable to that in control groups. Cold urticaria is an extremely chronic disease. The mean disease duration was 9.3 years. Serum antibodies to Epstein-Barr virus, measles virus, cytomegalovirus (CMV), varicella-zoster virus (VZV), herpes simplex virus (HSV), Chlamydia psittaci and Mycoplasma pneumoniae were determined in all 39 patients and compared with control groups. The EBV-antibody patterns (heterophile antibodies and different types of EBV-specific antibodies) showed no evidence of current or of recent primary or secondary infection with EBV. Complement fixing antibody titres to measles virus, CMV, HSV and Mycoplasma pneumoniae were significantly higher in cold urticaria patients than in controls. The existence of a basic immuno-regulatory defect responsible for both the cold urticaria and the elevated antibody levels is proposed.