In a process for producing butanediolformal (a good solvent which is used in the production of plastics and can also be used as a comonomer for the prodn. of polyformaldehyde) the mixture of 1,4-butanediol and HCHO used as starting material is produced by continuously bringing 1,4-butanediol in circulation into contact with a HCHO or trioxan-contg. gas until the HCHO butanediol molar ratio is >=1:1.
