Abstract: A seat mounting structure is provided including a stationary base and a generally horizontal seat support assembly disposed above the base. Spring controlled pivoted levers and connecting links support the assembly above the base for vertical movement relative thereto between upper and lower limit positions while maintaining the seat support generally horizontally disposed. Controlling springs of the seat mounting structure include a first pair of springs which are progressively tensioned as the seat support assembly is moved from its upper limit position to its lower limit position and a second pair of springs which are pretensioned and which are further tensioned, considerably more gradually than the first pair of springs, as the seat support assembly is moved from its upper limit position to its lower limit position. In addition, adjustment structure is provided whereby the tension of the first and second pairs of springs may be rapidly and selectively adjusted.