LongoVital (LV) (DK. reg. no. 5178/75) is a herbal based tablet enriched with recommended doses of vitamins. The present study was undertaken to investigate prevention of recurrent aphthous ulceration (RAU) during daily intake of LV for six months as compared with placebo in a double-blind, randomised clinical, cross-over 1-year study. The population comprised 29 otherwise healthy minor RAU patients (18F, 11M) mean age 36 (18-67), with an estimated average number of recurrences the previous year of 12.8 (3-30). The number of recurrences was significantly reduced on treatment with LV during the latter four of the six months (p less than 0.01) where 31% were totally free of recurrences. Subjective all-over evaluation of treatment period was significantly in favour of LV. LV induced no adverse reactions and is the first harmless systemic treatment which has proved better than placebo in the prevention of RAU.