A drop-on-demand printing method comprising performing the following steps in a printing head: discharging a first primary drop (x21A) of a first liquid to move along a first path; discharging a second primary drop (x21B) of a second liquid to move along a second path; controlling the flight of the first primary drop (x21A) and the second primary drop (x21B) to combine the first primary drop with the second primary drop into a combined drop (x22) at a connection point (x32) within a reaction chamber within the printing head so that a chemical reaction is initiated within a controlled environment of the reaction chamber between the first liquid of the first primary drop and the second liquid of the second primary drop; and controlling the flight of the combined drop (x22) at least by means of a stream of gas (x71A, x71B).