LongoVital (LV) (DK. reg. no. 5178/75) is a herbal-based tablet enriched with recommended doses of vitamins. Peripheral lymphocyte subsets: T-helper/CD4 (OKT4+) and T-suppressor/cytotoxic/CD8 (OKT8+) were studied quantitatively in 31 otherwise healthy patients with minor recurrent aphthous ulceration (RAU) during six months' daily LV intake in a double-blind, randomised, crossover 1-year study. Fourteen had had LV during the first six months (GrA) and 17 LV during the latter six months (GrB). OKT4+ percentages increased significantly during the LV period in both groups (p less than 0.05). OKT8+ percentages increased in both groups, however, only significantly in GrA (P less than 0.05). It is concluded that LV acts as an immunostimulator in patients with RAU and that the increase in T-lymphocyte subsets may account for the previously reported benefit of LV in RAU prevention.