otal proteins extracted from wild-type plants of Arabidopsis thaliana Heyhn, an etiolated mutant, a de-etiolated mutant and a mutant affected in cotyledon morphology, were analyzed by two-dimensional gel electrophoresis. Computer analysis of two-dimensional gels allowed the characterization of the mutants by a set of proteins showing a differential expression when compared with the wild-type plant grown under the same conditions. The overlap between comparisons of the different mutants with the wild-type allowed the identification of groups of polypeptides which, since their expression is altered in several mutants, might be involved in certain physiological functions. For example, this approach showed a possible involvement of actin in the elongation process. The simultaneous analysis of the two-dimensional protein patterns of different mutants seems, therefore, to be a promising approach to characterize proteins involved in various physiological functions.