Variability of expression of formate dehydrogenase (FDH) caused by uptake of C-1 compounds was examined by using Arabidopsis thaliana as a model plant. Effects of uptake of several C-1 compounds were evaluated by Northern blot analysis using cDNA of A. thaliana FDH prepared by cloning on the basis of known sequence. As a result, expression of the FDH gene in A. thaliana was not intensely influenced by formic acid, an inherent substrate for FDH, but strongly induced by its reduced form, formaldehyde.