A protocol involving the combination of liquid-phase isoelectric focusing and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was developed. Liquid-phase isoelectric focusing was used to separate serum peptides and proteins into 20 different fractions based on their pl values using a Rotofor apparatus. A total of 2 ml of blood was subjected to fractionation. The results from replicate Rotofor runs indicate that the Rotofor fraction a protein appeared in varied from run to run.