A dispenser head (104) is fitted on two separate reservoirs which are disposed side-by-side and on the outlet openings whereof, dispenser valves are disposed. The head (104) comprises a first part (113) which cooperates simultaneously with the two valves with a view to producing the ejection of each one of the constituents into an ejection duct which passes through it. The second part of the head is complementary to the first part so as to constitute in the assembled position of the two parts, a mixing chamber (134) into which there open the two ducts (121a, 121b). The mixing chamber opens out to the outside of the head. Deflectors (136) may be carried by one of the parts (113, 114) in the mixing region of the chamber (134) to improve the mixing of the material dispensed from the two reservoirs.