Abstract: A pharmacologically active cyanoguanidine derivative, generally referred to as cimetidine, is prepared by causing 4-methyl-5-hydroxymethylimidazole or a salt thereof to react with 2-substituted-1-methyl pyridinium salt and then causing the intermediate reaction product to react with N-cyano-N'-methyl-N"-(2-melcaptoethyl)-guanidine. The initial and subsequent reactions are carried out at room temperature under atmospheric pressure, using one and the same reaction vessel. No isolation of the intermediate reaction product resulting from the first reaction is required preparatory to the subsequent reaction. The recovery of the final intended product is carried out without using a column chromatography.