Abstract: There is provided herein an improved, more continuous, low pressure ethynylation process for the production of butynediol which comprises first continuously reacting formaldehyde and acetylene in a reaction zone at low pressures, in a stirred aqueous medium, in the presence of a finely-divided ethynylation catalyst, to form a reaction product mixture containing butynediol and catalyst slurry. Then the reaction product mixture is withdrawn and continuously and simultaneously filtered and concentrated to form two streams, a catalyst-free filtrate stream and a flowable, concentrated catalyst slurry stream, the latter being capable of immediate recycling to the reaction zone without further treatment. The filtrate stream containing the butynediol is available for purification and further operations.