The addition of appropriate quantities of finely divided solids to hydrocarbon, silicone, and glycerol base lubricants has been found to increase their life in stopcocks manyfold. The flow properties of the dispersions show that those solids that materially increase the high shear viscosity, without contributing greatly to the thixotropy of the system, are the most effective. This effect is produced by solids that have a polarity similar to that of liquid vehicle and are readily wetted by the vehicle. Under these conditions, a linear relation exists between the viscosity of the lubricants at a mean rate of shear of 1000 sec.–1 and their life in the stopcock.