Three dimensional isobolograms of three–way mixtures of site–selective anaesthetics that either (a) act on a single site or (b) act on different sites show additivity and synergy, respectively. The triangular grey surface is the result expected for additivity (Surface of add.). (a) The drugs corresponding to the x, y, and z axes are: for the Site 1 agents, azietomidate, etomidate, and carboetomidate; for the Site 2 agents, R‐mTFD‐MPAB, R‐miPr‐MPAB, and R‐mCF3‐MPAB and for the Site 3 agents, THDOC, 3α5βP, and alphaxalone. (b) Data shown are from experiments where etomidate was varied and the other two (alphaxalone and R‐mTFD‐MPAB) were held constant, where R‐mTFD‐MPAB was varied while the other two anaesthetics were held constant and where alphaxalone was varied and R‐mTFD‐MPAB and etomidate were held constant.