Chemicals that bind to protein may cause immunological responses that include allergic contact hypersensitivity mediated by T cells. Various animal models have been used to predict chemical-mediated contact sensitization. One assay that has recently been developed utilizes the proliferation response induced in the draining auricular lymph node after exposure to contact sensitizers. This assay has been modified to a simpler method that results in the more rapid processing of samples with greater reproducibility. Isothiazolones are chemicals used as biocides in various applications which at greater than use concentrations may cause allergic contact hypersensitivity. The mouse auricular lymph node cell proliferation assay has been used to examine the potential of various isothiazolones to induce contact sensitization. The extent of lymph node cell proliferation was dependent on the concentration of isothiazolone, the vehicle used in the application, and the ability of isothiazolone to bind to protein. Kathon biocide contains two isothiazolones: 5-chloro-2-methyl-4-isothiazolin-3-one (CMI)2 and 2-methyl-4-isothiazolin-3-one (MI). In vivo studies have shown that protein binding correlates with auricular lymph node cell proliferation and an increase in auricular lymph node size. CMI, which binds to protein, induced an auricular lymph node cell proliferation response while MI, which poorly binds to protein, neither stimulated a proliferative response nor induced an increase in lymph node size at concentrations similar to CMI.(ABSTRACT TRUNCATED AT 250 WORDS)