SUMMARYA simple method for concentrating psittacine beak and feather disease virus (PBFDV) from crude feather suspensions is described. The addition of 10% polyethylene glycol (MW 6000 to 9000) to feather suspensions facilitated the precipitation and pelleting of PBFDV by low speed centrifugation. Pellets were resuspended in one-twentieth of the original volume with caesium chloride (CsCl) buffer and subjected to isopycnic ultracentrifugation. Peak haemagglutination activity (HA) occurred at 1.35 g/ml in PBFDV CsCl gradients. CsCl purified virus agglutinated galah (Eolophus roseicapillus), eastern long-billed corella (Cacatua tenuirostris), sulphur-crested cockatoo (Cacatua galerita), Major Mitchell's cockatoo (Cacatua leadbeateri) and gang gang cockatoo (Callocephalon fimbriatum) erythrocytes, but not those of 19 other avian or five mammalian species. PBFDV agglutinated galah erythrocytes at 4°C and 37°C over a wide range of pH and no change in HA titre was observed when PBFDV was treated with chloroform. HA persisted in PBFDV suspensions heated to 80°C for 30 min, but was not detected after incubation at higher temperatures. High HA titres were detected in the feathers, serum, liver and kidneys of PBFD-affected birds.