A process is described for extracting gram-negative integral membrane proteins from bacteria or bacterial host cells containing a recombinant vector by differential detergent tangential flow diafiltration. This process has several advantages over alternate processes. First, it combines the clarification and extraction processes into one unit operation. The product is extracted from the cells and it is separated from cell debris with only one continuous diafiltration process. Second, the membrane proteins are extracted in a semi-purified state, which simplifies the downstream processing steps. Third, this process is very scalable because the only requirement is that the surface area of the membranes be increased proportionally with the amount of cells.