An enzyme-linked immunosorbent assay for the measurement of antibodies directed against Pseudomonas aeruginosa cell surface antigens was developed. Formalin-killed whole cells of P. aeruginosa, adsorbed to polystyrene acrylic copolymer cuvettes, were used as immobilized antigens. Antisera to P. aeruginosa mucoid strain 144M and to its spontaneous nonmucoid derivative, 144NM, were raised in rabbits by immunization with Formalin-killed bacteria. By using this enzyme-linked immunosorbent assay, anti-144M serum was found to have a ca. 10-fold-higher antibody titer to 144M than did anti-144NM serum, suggesting that 144M may have either immunogenic determinants not present on 144NM or perhaps simply more antigenic determinants. In contrast, anti-144M and anti-144NM immune sera were found to have nearly identical antibody titers to 144NM, suggesting that these strains share many determinants. Anti-P. aeruginosa immune serum was found to contain Pseudomonas-specific antibodies as well as antibodies which cross-reacted with other gram-negative bacteria. Finally, absorption studies demonstrated that this assay can detect both LPS and non-LPS surface-exposed antigenic determinants. Thus, this whole bacterial cell enzyme-linked immunosorbent assay should prove useful in monitoring patient sera and secretions for potentially protective immunoglobulins directed at P. aeruginosa cell surface antigens.