The evaluation of the usefulness of DNA probes in a diagnostic setting to identify nuclear inclusions in selected viral infecciöns (psittacine beak and feather disease viral infecciön, avian polyomavirus infecciön, adenovirus infecciön and Pacheco's parrot disease) is reported. A DNA in situ hybridization method was used to detect viral nucleic acid in sections of paraffin-embedded tissues coming from birds naturally and/or experimentally infected. It is concluded that DNA probes used for polyomavirus (FN-19) and adenovirus (FN-23) are able to identify nucleic acid of each virus in the cells with nuclear inclusions, and when used for psittacine beak and feather disease virus (FN-8), and Pacheco's parrot disease virus (FN-49) are able to detect viral nucleic acid in cells with or without inclusions. © 1994, Taylor & Francis Group, LLC. All rights reserved.