DNA conformational switching between B and Z forms was controlled with tilorone (intercalator) and sulfocalix[8]arene (C8AS, receptor for tilorone). When tilorone was added to the Z-DNA that had been beforehand induced by cobalt hexamine , the conformational transition from Z to B form was induced. The resultant B-DNA was turned back to Z-DNA by adding C8AS. This change was a clear-cut transition because most of the intercalated tilorone molecules were pulled out and captured by C8AS. This mechanism was established by isothermal titration calorimetry in which the binding constant of tilorone to C8AS was shown twice larger than that of tilorone/DNA.