Latex allergy is now known to be related to type I hypersensitivity. In latex products, several reports have identified at least 10 allergens. However, 56 polypeptides have been shown to react to IgE by two-dimensional gel electrophoresis and immunoprints. All studies using immunoprints have analyzed a relatively small number of sera. The aim of the present study was to analyze the specificity and the isotypic expression of a wide sample of latex-sensitive patients. Latex proteins were separated by SDS–PAGE in an 8–18% gel gradient, transferred onto a nitrocellulose sheet by Western blot, and revealed by serum from latex-sensitive patients. The presence of IgE, IgA, IgG1, IgG2, IgG3, and IgG4 was analyzed for each of the 54 sera. The results showed Hev b 3 to be the most frequently recognized protein, followed by Hev b 1, Hev b 7, and molecules of 94 kDa and 6–8 kDa. The most common isotypic association was IgE-IgG1, frequently with IgA. IgG4 was also present in a little less than half of the IgE-positive sera. IgG3 was also expressed but frequently recognized nonallergenic molecules. IgG2 was present in only two cases. Thus, as several authors have proposed a protective role for IgG in the allergic reaction, it may be of interest to compare these results with the course of the disease.