['To select the effective siRNA which could inhibit the expression of DNA methyltransferase 1 (DNMT-1) in adenoid cystic carcinoma (ACC) and discuss the time-, and dose-dependent effect of RNA interference (RNAi).', 'Four pairs of siRNA were designed, synthesized and transfected through oligofectamine reagent into ACC cell lines ACC-2, ACC-3 and ACC-M. 24, 48 and 72 h after transfection, total RNA and protein were harvested respectively. mRNA and protein expression level of DNMT-1 were detected by real time PCR, RT-PCR and Western blot, and then the effective siRNA was subsequently selected. ACC-3 as also transfected by different concentration of siRNA and the dose-dependent effect of RNAi was discussed. Cy(3) labelled GAPDH siRNA was used as a positive control.', 'Two of 4 pairs of siRNA inhibited the mRNA expression of DNMT-1 in three ACC cell lines and the expression of DNMT-1 was downregulated by 67%, 86%, 92% and 76%, 76%, 86% respectively. The gene inhibition was detected at 24 h or 48 h after transfection, maintained only 1 - 2 days and showed direct relationship to the concentration of siRNA. The change of protein expression level of DNMT-1 was consistent to the changes of mRNA.'] Does [ Synthesized small interfering RNA inhibit the expression of DNA methyltransferase 1 in salivary adenoid cystic carcinoma ]?