Recent reports suggested immuno cross-reactivity between natural rubber latex (NRL) and gutta percha proteins.  However, these proteins originate from very different sources.  NRL consists of polymers of cis-1,4-polyisoprene from the Hevea brasiliensis rubber tree, whereas gutta percha, an endodontic root canal filling material, is from the Palaquium gutta rubber tree consisting of trans-polyisoprene polymers.  Objectives:   This study was designed to assess cross-reactivity between antigenic proteins derived from gutta percha and NRL using an inhibition ELISA assay (ASTM D6499-00).  Methods:  Aqueous protein extracts were prepared from ammoniated and non-ammoniated raw gutta percha, thirteen brands of gutta percha points, and NRL gloves.   Results: Total water-extractable protein concentrations by a modified Lowry assay (ASTM 5712-99) exceeded 200 μg/mL for raw gutta percha.  However, gutta percha points ranged from 2 to 59 μg/mL, with a median value of about 3 μg/mL.  Water soluble protein is not readily extracted from gutta percha points.  After incubation with NRL antibodies, none of the gutta percha extracts were reactive.  On the other hand, similar NRL glove extracts were highly reactive.  Conclusions:   This study demonstrates that there is no immunologic cross-reactivity between raw gutta percha, gutta percha points, and proteins derived from NRL gloves.  Thus exposure to gutta percha endodontic points does not appear likely to initiate immediate hypersensitivity in individuals sensitized to NRL proteins.