An indirect immunoperoxidase method for the detection of herpesvirus in the liver and digestive tract of two psittacines (Ara macao and Cacatua sulphurea) with Pacheco's disease is described. The anti-Pachecovirus antiserum used was obtained from hyperimmunized specific pathogen-free chickens. It is concluded that this easily executed technique yields reliable results, allows a firm diagnosis of Pacheco's disease to be made and it would be suitable for investigating the pathogenesis of Pacheco's disease. © 1992, Taylor & Francis Group, LLC. All rights reserved.