A flow-through finite-dose diffusion cell has been designed for use in transdermal drug delivery research. The diffusion cell consists of an upper donor chamber and a lower receiver compartment through which a continuous supply of fresh solvent flows. The flow is directed to an automatic fraction collector. To validate the flow-through cell, its performance was compared directly against that of a conventional single-reservoir Franz cell. Homologous alkyl p-aminobenzoates were diffused through dimethylpolysiloxane membranes, and permeability coefficients increased with increasing chain length, reaching a plateau at the butyrate ester for both types of cells. This behavior suggests a shift from membrane-controlled diffusion to boundary layer control. Permeation of the butyrate and valerate compounds was significantly faster when the flow-through cell was used, suggesting that better mixing is obtained through the flow-through cell design. Considering the advantages offered in terms of time and labor saved through its use, the flow-through cell with automatic fraction collector appears to be a viable alternative to the conventional Franz cell.