A minidevice for performing gel-free proteome prefractionation via conventional IEF in soluble carrier ampholyte buffers is reported here. It consists of a compact block of poly-oxymethylene in which eight samples and two electrode chambers are machined. Each of the eight sample chambers can be filled with up to 120 mL of sample and has the following size: 7 mm width, 3 mm depth and 10 mm height. The anodic and cathodic compartments have the same width and height as the sample chambers, but with a depth of 6 mm, thus accepting up to 250 mL of electrodic solutions. Focusing is in general accomplished in 2 h with a voltage gradient of up to 1000 V (7 cm electrode distance). Easy fractionation and collection of the content of the eight chambers is achieved by simply pressing a rubber diaphragm against the edges of the thin walls separating each well, this automatically breaking liquid continuity. The performance of this device has been tested by sub- fractionating total cell lysates of a human cancer cell line (U2Os) and of Escherichia coli bacterial cells, and by analysing the content of each chamber by mono-dimensional SDS- PAGE and 2-D maps.