Thirty Pseudomonas aeruginosa strains were isolated from the sputa of cystic fibrosis patients. In each culture supernatant, the amount of three exoproteases (LasA, alkaline protease and elastase) was determined using immunochemical procedures. These assays used selected peptide-MAP (multiple antigen peptide) strategy as antigen for animal immunisation. The method appeared to be reproducible, simple, sensitive and specific without cross-reactivity between the antisera. The resulting values differed from one strain to another mostly for elastase production. Despite the fact that four genes (lasA, lasB, lasR and rhlR) were shown to be necessary for full elastolytic activity, it was obvious that if LasA was not secreted in a naturally non-elastase-producing strain, in return in an elastase-producing strain, there were no apparent relationships between LasA and elastase production and between LasA and alkaline protease secretion. Furthermore, in vitro, the secretion of the three exoproteases seemed to be independent of the mucoid or non-mucoid phenotype of the bacteria.