An indirect immunofluorescence technique was developed to detect antibodies to ds-DNA in a dog affected by Systemic Lupus Erythematosus (LES). The assay was based upon the use of the antigen substrate Trypanosoma theileri, isolated from samples of bovine blood and maintained in culture tubes. Slides were prepared by the drop method and maintained at -20 degrees C until used. This T. theileri immunofluorescence test, evaluated with positive and discriminant results in a previous study on human sera affected by LES, was used for the first time in the diagnosis of canine LES. The results indicate that T. theileri IFA is specific and reliable.