Microcavities provide a well-controlled flow-free microenvironment and thus play an important role in many microfluidic systems, for example in the form of cell-culturing microchambers. Here we show that transient concentration gradients that emerge during diffusive exchange of solutes in microcavities can induce noticeable passive migration of blood cells and synthetic phospholipid vesicles, an effect that has been broadly termed as diffusiophoresis. We observed migration during the exchange of different electrolyte and non-electrolyte solutions that all had the same osmolarity. Depending on the type of solutions, cells and vesicles migrated towards the entrance or towards the end of the cavity, with migration distances on the order of ten micrometres. Thus, the observed phenomena can significantly affect cell behaviour in many applications of microfluidic devices in biomedicine and biotechnology.