Three classes of cell wall-defective mutants of the unicellular green alga Chlamydomonas reinhardtii have been described in the literature differing with respect to the amounts of cell wall material and its attachment to the plasma membrane, respectively. We have compared the production of the chaotrope-soluble cell wall polypeptides by the different mutants. These experiments have been performed by comparative Western-blot analyses using antibodies raised (1) against the deglycosylation products of the insoluble wall fraction of wild-type cells, (2) against the deglycosylation product of the '150 kDa' chaotrope-soluble cell wall polypeptide and (3) against the carbohydrate side chains of the Chlamydomonas cell wall glycoproteins, respectively. Considerably different levels of cell wall polypeptides were found in the LiCl-extracts from intact cells of the various mutant strains containing the apoplastic, chaotrope-soluble cell wall glycoproteins. No correlation was found between the amounts and the patterns of cell wall glycoproteins present in the LiCl-extracts and the electron microscopical classification of the mutant strains. All the mutant strains were shown to contain the same amounts and patterns of intracellular cell wall precursors as wild-type cells as revealed by Western-blot analyses of urea-SDS lysates of LiCl-pretreated cells. These findings indicate that the different mutant strains produce the same set of cell wall polypeptides at the same relative amounts as wild-type cells. However, in the case of some strains belonging to different classes of cell wall mutants and showing differential seggregation patterns in crosses, alterations were observed for the pattern of extracellular cell wall polypeptides present in the LiCl-extracts from intact cells and in the culture medium, respectively.