Using a cellulose dialysis membrane and aqueous solutions of common drugs as a proof-of-principle example, we demonstrate that solid but permeable and flexible membranes can be used as interfaces for the direct analysis of solution constituents via easy ambient sonic-spray ionization mass spectrometry. This new combination of MS techniques, herein termed EASI-MIMS, promotes droplet pick up of the analyte from the external surface of the membrane from where the analyte has selectively permeated for proper mass spectrometry characterization and quantitation. Possible application of EASI-MIMS such as the environmental analyses of effluents, on-line monitoring of fermentation and biotransformations and on-line pharmacokinetic blood analysis are discussed.