A prosthesis socket casting device having a housing and a flexible membrane for receiving a residual limb, the housing and the membrane defining a cavity for containing a fluid. Within the housing are means that are a function of the patients weight for altering the distribution of the reactive fluid pressure applied when the residual limb is received within the membrane. In a preferred embodiment, the altering means comprise a movable piston that is provided at a lower end of the housing.
