P-protein bodies (forisomes), in phloem cells of legumes, transform the chemical free energy of their reaction with alkaline earth metal ions into mechanical energy. In addition to using the bending of glass fibers, micromechanical forces generated by the switching of forisomes in aqueous solutions were measured by monitoring the bending of microscale polymer cantilever beams. The forisomes were fixed by chemisorption to the tips of four orthogonal beams of a BioMEMS microsystem designed and manufactured using the process of sacrificial layer micromolding. The sensor layout allows force measurements in the longitudinal and radial direction of the forisomes. For different forisomes a longitudinal force in the range from 84-136 nN and a radial force of 22-61 nN were measured.