Eight captive-bred horned parakeets (Eunymphicus cornutus) and four captive-bred Major Mitchell cockatoos (Cacatua leadbeateri) from the same aviary tested positive for psittacine circovirus (PsCV) DNA in whole blood by nested-polymerase chain reaction (PCR). The chronic form of disease with feather fragility and loss was observed in three horned parakeets. Infection in other individuals was subclinical. Immunosuppression, either hematologically or as susceptibility to secondary infections, was not observed. Treatment consisted of the administration of beta-(1,3/1,6)-D-glucan from oyster mushroom (Pleurotus ostreatus). Excluding two accidentally dead parakeets, four out of the original six horned parakeets, and all Major Mitchell cockatoos were negative for PsCV DNA in whole blood in 7-9 mo after the treatment was started. Even though the absence of PsCV DNA in blood does not signify elimination of the virus from the whole organism, these preliminary results indicate a possible effect of beta-glucan in the treatment of PsCV infection. To the author's knowledge, this is the first report of PsCV in horned parakeets.