A simple method for the affinity isolation of lymphocyte subpopulations using nylon wool as a solid phase matrix is described. This matrix was coated with an acid-treated IgG fraction of polyclonal antibodies against mouse immunoglobulins. Using this approach, a simple isolation procedure for lymphocyte subpopulations, yielding purities higher than 95% was developed. The method can be used on a large scale for positive and negative cell selection, with very little non-specific binding. The isolated populations are fully functional.