The isothermal sections of the Co–Ni–Ti system at 950 and 1 000 °C were investigated experimentally. Diffusion couples were measured by electron probe microanalysis to construct the phase relations at 950 °C, whereas eleven key alloys annealed at 1 000 °C were investigated using X-ray diffraction and electron probe microanalysis. The ternary phase, τ-(Co,Ni) 3 Ti (hP24-VCo 3 ), was observed at both temperatures. At 950 °C, continuous solid solutions are formed between CoTi 2 and NiTi 2 as well as between CoTi and NiTi. Eight 3-phase regions, i. e. Ni 3 Ti + (Co,Ni)Ti + τ, Ni 3 Ti + γ-(Co,Ni) + τ, τ + c-Co 2 Ti + (Co,Ni)Ti, τ + c-Co 2 Ti + Co 3 Ti, τ + Co 3 Ti + γ-(Co,Ni), c-Co 2 Ti + h-Co 2 Ti + Co 3 Ti, L + β-(Ti) + (Co,Ni)Ti 2 and L + (Co,Ni)Ti 2 + (Co,Ni)Ti, were constructed at 1 000 °C. Considerable ternary solubilities in Ni 3 Ti, Co 3 Ti and c-Co 2 Ti were determined.