Abstract: An adjustable matrix wheelchair seat can be mounted on a pair of rods such as are provided on the seat rails of a typical wheelchair or on any pair of rods adapted to be rigidly fixed to and aligned in a longitudinal direction relative to the frame of the wheelchair. A lateral array of spaced apart substantially inelastic straps is extended between and engaged on the rods. A longitudinal array of spaced apart substantially inelastic straps is engaged on the forwardmost and rearwardmost straps of the lateral array. The longitudinal array traverses the lateral array to define a horizontal matrix of ventilating interstices. The length of any or all of the straps of the lateral and horizontal arrays is independently adjustable to permit alteration of the pressure pattern imposed on the arrays by the patient occupying the seat.