A systematic study of immunoglobulin G (IgG) immobilization on Langmuir-Blodgett films has been carried out with the aim of characterizing the immobilization efficiency and the protein activity. A quantitative evaluation of the amount of immobilized protein has been carried out by IR spectroscopy. Maximum IgG immobilization (400-900 ng cm-2) has been obtained with buffers of low ionic strength (0.005 M) and pH near but below the isoelectric point of the protein. No desorption has been observed in pure water, but in buffers desorption increases with the ionic strength of the buffer. The probable mechanism of desorption is a screening of the charges responsible for protein attachment, by small ions from the buffer. As expected, this desorption leads to high non-specific binding (75% in 0.1 M buffer) by dynamic protein exchange.