The reaction of 2-aminobenzimidazole with selected 4-methoxy-,2,4-dimethoxy-, 4-chloro-, 4-nitro-, and 2-nitrocinnamic acid under different conditions has been described. Two series of derivatives were obtained: 4-aryl-1,2,3,4-tetrahydropyrimido[1,2-a]-benzimidazol-2-ones (1-3) or substituted amides 4, 5, 7. The following compounds: 4-(p-methoxyphenyl)- (1), 4-(2,4-dimethoxyphenyl)- (2), 4-(p-chlorophenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazo l-2-one (3), amides: 2-(p-nitrocinnamoylamino)- (4), 2-(p-methoxycinnamoylamino)-benzimidazole (5), and 3-methyl-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazol-2-one (6), recently synthesized, have been selected for further studies. Among the studied compounds, 3 and 4 strongly inhibited PHA-induced proliferation of human lymphocytes and weaker, but significantly, MLC-induced lymphocyte proliferation. 3 and 4 inhibited also LPS- or MLC-induced TNF-alpha production. In addition, TNF-alpha production, induced by LPS, was inhibited by compounds 1 and 2. Higher activity of 3 and 4 could be associated with the presence in their structures of -Cl and -NO2 substituents as compared with compounds possessing -OCH3 groups. Compounds 3 and 4 were not toxic when administered orally to mice which predisposes them for further investigations with a chance of clinical application.