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Quick response water potential and nondestructive water content measurements indicate that during transient, nonhysteretic flow of water following a rapid change of water content at one end of a horizontal column of soil, the soil moisture characteristic curve is a unique function during sorption from a particular initial water content, but during desorption there is a multiplicity of curves. These transient curves depend on the magnitude of the imposed water content change and also on the speed with which static equilibrium is achieved after the change. The consequences of this behavior are discussed in terms of diffusion theory, and it is concluded that it would be unwise to apply this theory to desorption situations until the quantitative significance of this behavior is determined for other materials.