Abstract: The invention relates to the new monohydrate of N-methyl-N'-{2-[(5-methylimidazol-4-yl)-methylthio]-ethyl}-N"-cyanoguanidi ne (cimetidine), a histamine-H.sub.2 receptor antagonist which is called N-methyl-N'-{2-[(5-methylimidazol-4-yl)-methylthio]-ethyl}-N"-cyanoguanidi ne H (cimetidine H) as well as to a process for the preparation of same, which comprises pouring a hot, homogeneous aqueous solution of N-methyl-N'-{2-[(5-methylimidazol-4-yl)-methylthio]-ethyl}-N"-cyanoguanidi ne, optionally containing also methylamine, onto ice and separating the N-methyl-N'-{2-[(5-methylimidazol-4-yl)-methylthio]-ethyl}-N"-cyanoguanidi ne monohydrate.

Abstract: 4-[(3,4-Dialkoxyphenyl)alkyl]-2-imidazolidinone derivatives having the formula I ##STR1## wherein R.sup.1 stands for a cycloalkyl group containing from 3 to 6 carbon atoms or benzyl group;R.sup.2 stands for hydrogen atom or an alkyl group containing from 1 to 4 carbon atoms;R.sup.3 stands for hydrogen atom or an alkyl group containing from 1 to 4 carbon atoms;R.sup.4 stands for hydrogen atom, or an alkyl group containing from 1 to 4 carbon atoms or an alkoxycarbonyl group containing from 1 to 4 carbon atoms; andR.sup.5 stands for hydrogen atom or an alkoxycarbonyl group containing from 1 to 4 carbon atoms,are prepared by(a) reducing a hydantoin derivative having the general formula II, wherein R.sup.1 and R.sup.2 are as defined above, with lithium aluminum hydride in a neutral organic solvent, or(b) hydrogenating catalytically an 1,3-dihydro-2H-imidazol-2-one derivative having the general formula III, wherein R.sup.1 and R.sup.3 are as defined above, while the meaning of R.sup.