Altogether 173 patients with warts were under observation for at least 3 and in most cases 6 months. In 80% of the patients wart-virus antibodies were present and could be measured by immunodiffusion (I.D.) and in 20% also by complement-fixation (C.F.) techniques. The mean duration of the warts in patients with C.F. antibodies was 0-6 years and in the others 1-9 years. The occurence of C.F. antibodies (IgG) was associated with rapid healing; 75% of these patients were cured during the first 2 months of the observation period. In contrast, of the patients with antibodies measurable only by the I.D. technique (IgM and/or low titres of IgG), only 16% were cured during the first 2 months and they had a fairly constant cure-rate (approximately 9% per month) during the 6 months' observation period. The results indicate that the cure of warts is partly connected with immunological phenomena, especially with the presence of C.F. antibodies. In other cases wart regression may be mainly a non-immune process, perhaps due to a limited lifespan of wart cells.