The diagnosis of natural rubber latex allergy begins with a clinical history and often involves a confirmatory test. While the puncture skin test (PST) has been regarded as a primary confirmatory test for the assessment of patients for IgE-mediated disease, the absence of an FDA-licensed Hevea brasiliensis latex extract in the USA has restricted its use in the diagnosis of latex allergy. Serological tests have therefore become critically important as alternative diagnostic tools. Three manufacturers have currently obtained 510K clearance from the FDA for their latex in vitro reagents: the CAP System (PharmaciaUpJohn); the AlaSTAT, (Diagnostic Products Corporation) and the HY- TEC assay (HYCOR Biomedical). Although all of these commercial assays are based on non-ammoniated latex (NAL) as their primary allergen, there are differences in their solid or soluble supports and detector systems. Paired comparisons of the three assays indicates that they disagree on the antibody status of an individual serum. This leads to patient's sera being "positive" by one or two tests and negative in (an)other(s). It is speculated that the disagreement among tests is due to IgE antibody assays detecting different subsets of IgE antibody of a given specificity, possibly as a result of differential specificities of their allergen-containing reagents. Reasons for this include variability in allergen content in different batches of source latex; sensitized individuals producing specific IgE antibody to at least 8 Hevea allergens, Hev b 1-Hev b 8, each of which differs in its structure, size, net charge (pI), relative allergenicity and abundance in natural rubber latex. The relative content and ratios of Hevs in the final allergen preparation most probably could enhance the diagnostic accuracy of a specific test. Other potential causes of allergen-containing reagent heterogeneity include variable stability during storage and variable binding of allergen to labels (e.g., biotinylated co-polymer in AIaSTAT) or solid supports (sponge in CAP; cellulose disc in HYTEC). Using receiver operating characteristic (ROC) curve analysis, and positive PST to NAL as the discriminator, the HY-TEC system has significantly greater (P<0.01) area under the curve (AUC, 0.924 + 0.017, standard error) than CAP (0.869 + 0.024) or AlaSTAT (0.858 + 0.024), suggesting it may be more accurate under the comparison conditions evaluated.