A classification of one-dimensional electrophoresis gels was achieved using a fast approximation of the Karhunen-Loeve transformation. The algorithm was based on wave packet decomposition theory, using in particular quadrature mirror filters derived from orthogonal bases of wavelets. Bacterial proteins from two different species of staphylococci were separated by SDS-PAGE electrophoresis. The gel images were analyzed by computer and the protein bands were clustered, after an orthogonal projection onto a space of lower dimension, by standard statistical methods.