Colorimetrically using the MTT assay the cytotoxic activity of 5-aryl-1,2,3,4,5,6-hexahydrobenz[4,5]imidazolo[1,2-a]quinazolines and a tautomeric mixture of 4-amino-2-phenyl-6H-pyrido[1,2-a] pyrimidin-3-carbonitrile with 2-(phenyl(pyridin-2-ylamino)methyl)- malononitrile was screened. These compounds were obtained by the three-component condensation of aromatic aldehydes (benzaldehyde, 3-bromobenzaldehyde, 4-methoxybenzaldehyde), heterocyclic amines (2-aminobenzimidazole or 2-aminopyridine) and cyclohexanone or malonic acid dinitrile in comparison with the starting amines. Compounds were tested at concentrations of 100, 50, 25, 12.5, 6.25, 3.12, and 1.61 ?g/ml on monolayer cell lines of the African green monkey kidney (Vero). IC50 values for the most active compounds (5-(4-methoxyphenyl)-1,2,3,4,5,6- hexahydrobenz[4,5]imidazolo[1,2-a]quinazoline and a tautomeric mixture of 4-amino-2-aryl-6H-pyrido[1,2-a]pyrimidine-3-carbonitrile with 2-(phenyl(pyridin-2-ylamino)methyl)-malononitrile were 75 and 50 ?g/ml, respectively. For 5-phenyl-1,2,3,4,5,6-hexahydrobenz[4,5] imidazolo[1,2-a]quinazoline, the IC50 value was 100 ?g/ml. For the remaining compounds, IC50 was not detected, and the starting 2-aminobenzimidazole and 2-aminopyridine inhibited the metabolic activity by only 20–30% at maximum concentrations. The values of the half-inhibitory concentration determined using the MTT assay are similar to the values, which were obtained earlier in the cytotoxic studies of similar heterocyclic compounds by AlamarBlue assay.