This letter proposes a concept for frequency-reconfigurable slot antennas enabled by pressure-driven capacitive microfluidic switches. The switches are operated by pneumatically displacing a plug of eutectic gallium indium alloy (EGaIn) within an air-filled microchannel that traverses the slot orthogonally. Frequency reconfigurability is achieved by altering the displacement of conductive fluid within the channel, which reactively loads the slot. A transmission-line model is developed to capture the physical behavior of the fluid channel, and measurements are provided that show good agreement with the behavior of the model. \ 2002-2011 IEEE.