A relaxation dynamometer is described for the application of a constant force down to 30 nN on a body suspended in a fluid. Displacements are observed to within 1 pm. This has been applied to fluids including a silicone oil, glycerol at various temperatures and molten sodium isovalerate at 220°C. Illustrative examples include what appear to be critical limits preceding irreversible movement in the mesophase of sodium isovalerate.